In order for us to understand when Jesus will come we need to find out how old humanity is and for that we need to answer a couple questions:
39.How many years the Israelites were in Egypt?
40.How many years from Exodus to Solomon’s government?
(41. The application of  Jephthah).
42.When the Exodus took place?

39. How many years the Israelites were in Egypt?

Many people, who attentively have read Genesis and Exodus had noticed a strange contradiction in the Bible. In Ex.12:40 it is spoken: «Now the sojourning of the children of Israel, which they sojourned in Egypt, was 430 years».

However the genealogy which was given in the Bible, as we shall see later, does not match with the specified period of time.

So, for example, in Ex. 6:16-20 we see the genealogy of Kohath, who came in Egypt with his grandfather Jacob and father Levi (Gen. 46:11). In Egypt Kohath begat Amram. Amram begat Aaron and Moses, who during the Exodus were: Aaron 83 years old, Moses - 80 years old (Ex. 7:7).

If we will assume, that Kohath came in Egypt being an one year old baby, and then had begat Amram in the very year of his death at the age of 133 years (Ex.6:18). And Amram, in his turn, begat Moses in the very year of his death, at the age of 137 years (Ex. 6:20).  Even then we can not receive 430 years: 132+137+80 = 349 years. We are lacking of 81 years at least.

Also after birth of Amram Kohath begat Uzziel (Ex. 6:18), the sons of Uzziel came out of  Egypt with Moses (Lev.10:4). Here again we have the same loss of time.

Another example: As we will see later, Levi came in Egypt when he was 44-45 years old, there he begat Jochebed, who became the mother of Aaron and Moses (Ex. 6:20; Num.26:59). If we just imagine, that Levi begat Jochebed in the very year of his death, at the age of 137 years (Ex.6:16), i.e. (137-44 =) on 93-d year of his living in Egypt, then from 430 years of living in Egypt we shall subtract these 93 years and age of Moses, when he left Egypt (430-93-80=257) it will turn out, that Jochebed gave birth to Moses being 257 years old. It  is impossible, because in that time people did not live so long, and the birth of Isaac  by Sarah in the age of 90 was perceived as a miracle. Therefore, we are lacking at least 200 years to fill up 430 years period.

The Old Testament full of these kind of confusions. What the reason for the such contradiction?

It is necessary to note, that Ex.12:40 is the only place in the Bible, where it is spoken, the Jews were in Egypt during 430 years. Whether there are any other verses in the Bible, which could give a some answer for this dilemma? 

In Gal.3:16,17 it’s said: « to Abraham and his seed were the promises made … the law, which was 430 years after, cannot disannul». It means, the law appeared 430 years after God made the covenant with Abraham and his seed. The law was given at the mountain Sinai in two months after the exodus from Egypt (Ex. 19:1). The promise was given to Abraham, when he was 75 years old (Gen.12:4). It means from the time when Abraham was 75 years old to the Exodus is 430 years. 

In 25 years after the covenant was made, at the age of 100, Abraham begat Isaac (Gen.21:5). At the age of 60 Isaac begat Jacob (Gen.25:26). When Jacob came to Egypt he was 130 years old (Gen 47:9). Thus, from the time the covenant was made to the entering Egypt is (25+60+130 =) 215 years.

And, if from the covenant with Abraham to the law - 430 years, and 215 years have passed before the entering Egypt, it means, in Egypt the Jews were during 215 years.

Further you will see, that all Bible genealogies can not be placed in the frame of 430 years period  but perfectly can be placed in 215 -year's period.

At first- some Bible’s facts:

1. Out of 12 Jacob’s (or Israel’s) children 11 were born within 7 years. We know, Jacob had served Laban for 20 years (Gen.31:38,41). The first 7 years he worked for Laban’s daughter, Rachel, to marry her (Gen.29:18). After termination of those 7 years Jacob was deceived by Laban and instead of Laban’s  youngest daughter Rachel, he had married Laban’s older daughter Leah. After that he served Laban 7 years more (Gen.29:30). During those 7 years Leah gave birth to Jacob’s  7 children: Reuben, Simeon, Levi, Judah, Issachar, Zebulun and daughter Dinah. Two servants of Leah and Rachel birthed to him 4 more sons. After all Rachel delivered Joseph. (After birth of Joseph  Laban left Jacob to serve 6 more years (Gen.30:25). 7 years + 7 years + 6 years = Total 20 years of Jacob living at Laban’s house (Gen.31:38,41)).

Hence, the age difference between the oldest Leah’s son - Reuben, and Joseph was no more than 7 years, between Levi and Joseph - no more than 5 years, between Judah and Joseph - no more than 4 years.

2. At the age of 17 Joseph was sold by his brothers into a slavery (Gen.37:2,28). When he was 30 years old he decoded the pharaoh’s  dream about 7 fruitful and 7 hungry years. He was erected by the pharaoh as a ruler over all land of Egypt (Gen.41:46) and had married an Egyptian woman. Within the first 7 fruitful years, i.e. at the age of 31-37 years, Joseph begat Manasseh and Ephraim (Gen.41:50). In the second - third year of famine (Gen.45:6) Jacob with all family came to Egypt.

Thus, during the Jacob’s entering into Egypt  Joseph was (30+7 good years +2 hungry years +? 1) 39-40 years old. That means, Reuben was 46-47 years old, Levi - 44-45 years; Judah - 43-44 years.

3. Jacob came to Egypt in the age of 130 (Gen.47:9) with all his children, who by then already had their own children (Gen.46:8-27). 

-         Reuben (46-47years old) came with four sons (Gen.46:9), his second son Phallu could be approximately 3 to 27 years old. As we shall see further, Phallu, most likely, was less than 10.

- Levi (44-45 years old) came with his three sons (Gen.46:11), his middle son Kohath could be also about 3 to 25 years old. As we shall see further, Kohath, most likely, was very young: less than 10 years old.

- Judah (43-44 years old) had begotten 5 sons by then (Gen.46:12), his 4-th son Pharez (approximately 20-23 years old) already had two sons by his own. The oldest Pharez’s son, Hezron, could be about 2 to 6 years old. 

-Joseph (39-40 years old) begat his older son Manasseh at the age of 31-36 (during the first 7 years of plenty), so when Jacob arrived Manasseh was about 3-8 years old. To define how long Israelites were in Egypt, we shall look after genealogy of sons of Jacob’s  4 sons: Reuben, Levi, Judah and Joseph ("b" means: was born; one little square is 10 years). If we would assume the first son could be born from a man 20-70 years of age, the picture of births could look approximately as follows:  

You can see by yourself  that submitted genealogies  can not be placed into the 430-year's period, however they can be perfectly placed in 215-year's period.  

Some researchers try to increase the 215-year's period till 350 years however any other date, except for 215 years, can not stand the test by the Bible and the logic. So, for example, we know, that Levi came to Egypt in the age of 45. He had lived 137 years (Ex. 6:16). His daughter Jochebed gave birth to Moses, who was 80 years old when Exodus occurred. 

It is well-known that some women can gave births until 60. Let's assume Jochebed gave birth to Moses in her latest age - at 60. Let's assume also that Levi begat Jochebed at his age of 120 years old, at 75-th year of habitation of the Jews in Egypt. That means the optimal period of the Jews’ habitation in Egypt can not be longer than (at 75 -th year after entering Egypt Jochebed was born  + she was 60 years old when she gave birth to Moses+ Moses was 80 years old at the time of Exodus =) 215 years.       

It is important to note, that in the earliest Christian works it was always told, that the Jews were in Egypt for the period of 215 years. So, for example Jewish historian  Josephus Flavius, who lived in the first century A.D., in his well-known work “ Antiquities of the Jews” wrote that the Israelites left Egypt “four hundred and thirty years after our forefather Abraham came into Canaan, but two hundred and fifteen years only after Jacob moved into Egypt” (II. 15.2, Whiston, William, trans. (1974 reprint), The Complete Works of Flavius Josephus (Grand Rapids, MI: Baker) taken from http://www.apologeticspress.org/articles/610).

Josephus Flavius had access to very old documents formerly housed in the Temple of Jerusalem from which he draw an information of early Israelite history. His writings are dated hundreds of years before the Masoretic text of the Tanakh (Hebrew Old Testament) was completed in the fourth century A.D. It is the translation of the Masoretic text we use today.  

Besides Josephus’ works there are two other highly reliable ancient texts which were written  much earlier than the Masoretic text of Old Testament. These are  Samaritan Pentateuch (Samaritan translation of five books of Moses) and the Alexandrian copy of the Septuagint (the Greek translation of the Old Testament was completed in III century AD), in which Exodus 12:40 reads as follows: “Now the sojourning of the children of Israel and of their fathers, which they sojourned in the land of Canaan AND in the land of Egypt was 430 years” (Clarke, Adam (no date), Clarke’s Commentary on the Old Testament—Volume I: Genesis to Deuteronomy (New York: Abingdon-Cokesbury, pp. 358-359. Taken from http://www.apologeticspress.org/articles/610).

Somehow during the copying of the Bible these two passages:“they and their fathers” and “in the land of Canaan” were lost in the present copies of the Hebrew text, and the verse Ex.12:40 lost  the logical connection with the events, described in the Old Testament.

Besides Gal.3:17 there are other Bible verses, which also are making understandable that the 430-year interval represented not only the time Jews were in Egypt but the whole period from Abraham’s entering into Canaan all the way down to the Exodus from Egypt.  

Thus, in Gen.15:13,14 and Act.7:6 it’s spoken that God said to Abraham: “Know of a surety that thy seed shall be sojourners in a land that is not theirs, and shall serve them; and they shall afflict them four hundred years.” If the Jews were in Egypt for 430 years, and God spoke about 400 years, maybe God  was mistaken for 30 years? Of course, not.

This prophecy was not about Abraham, but about his descendants. The prophecy says, that the sojourn of Abraham’s children on somebody’s land and their oppression will be finished after 400 years.

However what Abraham’s children there was talking about? When the prophecy was given Abraham had no children. Then the Egyptian maid gave birth to Abraham’s son Ishmael.  At that time Abraham probably thought: « Whether or not he is mine seed, God spoke about?» Then his miracle son Isaac was born, and  Abraham did not know whether to count his oldest  son as his seed by his birthright, or to consider the younger son as his successor due to a  God’s miracle of his birth (Gen. 21:9-11). Only when Isaac  grew up a little and was weaned God had specified for Abraham, that his seed is not in Ishmael but in Isaac (Gen.21:8,12). Hence, the line of Abraham’ s descendants was determined at that day of the feast, which was made by Abraham in honor of Isaac weaning.  

So, when these 400 years for Abraham’ s descendants had begun? If we will subtract from 400 years 215 years of the Egyptian slavery, we shall receive 185 years. Let's try to count from the entering of Egypt 185 years back. So,  Abraham begat Isaac. When Isaac was 60 years old he begat Jacob.  Jacob, as it was already discussed above, came to Egypt in the age of 130 years: 60+130=190 of years, that is 5 years more than 185 years. It means, when Isaac was recognized by God as Abraham’s seed he was 5 years old.

For us the age of 5 years as age for Isaac’ weaning seems rather late. Today a latest age for a weaning is 3 years. Probably, at that time this period was longer. Probably, Sarah loved so much her late wonderful child, that she continued to breastfeed him as long as it was still acceptable. 5 years are a some kind of edge of a child’s life,  time for transition from a baby to a thinking person (compare Lev.27:5 and 27:6). It is possible, that such late weaning was a reason for Ishmael’s  mocking of Isaac (Gen. 21:9). Ishmael by then was 19 (Gen.17:24,25). If Isaac was only 2 years old, the conflict between him and Ishmael would not be so bad as it is shown in Gal.4:28,29.

Thus, the prophecy about 430 years (Ex.12:40) began from time, when God made the covenant with Abraham, and was finished, when the Jewish people left Egypt.
The prophecy about 400 years (Gen.15:13) began from that moment, when 5-year old Isaac was recognized as the seed of Abraham, and was also finished at the time of the Exodus.  

In Gen.15:13 it is said: “thy seed shall be a stranger in a land that is not theirs, and shall serve them; and they shall afflict them 400 years”. 

Some people interpreter that in Egypt Israelites were 430 years, but in the slavery there they were for 400 years. However we know, that Joseph was about 40 when Israelites came to Egypt and he died at age of 110 (Gen.30:22), 70 years after Jacob entered Egypt. Until then Israelites were in good care. Thus, not 30, but at least 70 years Jews were not slaves.  

We can not say that Israelites were afflicted for 400 years. However we can possibly say, that Isaac was afflicted by Ishmael (Gal.4:29), Jacob by Esau to the point he had to leave his father’s house; later he was afflicted by Laban to whom he worked for 20 years. Then Joseph was sold to the slavery. We can say, that Egyptians always despised the Jews (Gen. 43:32). However under the real affliction only Abraham’s great-grandsons were, when after death of Joseph Egyptians began to enslave the Jews. 

That is why it is more possible the phrase «400 years» was not attached to the last words about the affliction, and was given for all the time of Abraham’s descendants until the Exodus.  Thus, at first they were the strangers. Canaan wasn’t the land  neither Abraham, nor Isaac and Jacob. In Ex. 6:3,4 it’s told, that Canaan was for them « the land of their pilgrimage, wherein they were strangers ». See also Ps.105:12,13. They had no houses, they lived in tents and didn’t stay on one place all the time.

After that Israelites served to Egyptians (Gen.47:6), then they were afflicted (enslaved) – and all of these took place during the 400 years.

God said to Abraham: «And also that nation, whom they shall serve, will I judge: and afterward shall they come out with great substance. But in the fourth generation they shall come hither again » (Gen.15:14,16). So, it’s says, that after the slavery God will punish the nation, to whom the Jews served (these are - 10 plagues of Egypt). It’s told, there three generations of the Jews will live in Egypt. The fourth generation will come back to the promised land.

Jacob came to Egypt with all his sons. His generation was completed before the entering Egypt. His all sons were already married and had children by they own. Even his youngest son –Benjamin already had 7 sons and 3 grandsons. 

That means, it is necessary to begin to count the generations from those who grew and had their children in Egypt. In the genealogy given by Bible they are Kohath, Phallu, Zerah and Hezron.

Kohath came to Egypt  as child (1 generation), later he begat Amram (2 generation), Amram begat Aaron and Moses (3 generation). But neither Aaron, nor Moses had reached the promised land.  Only their sons (4 generations): Eleazar , son of Aaron (Num.20:28) and Moses’ sons Gershom, and Eliezer (1Chron.23:15) came to the promised land.

 Kohath (1 generation) begat Izhar (2 generation), Izhar begat Korah (3 generation). Korah rebelled against  Moses by the mountain Sinai and was killed, however his sons (4 generation) remained alive and came to the promised land (Num.26:10,11).

Kohath (1 generation) begat Uzziel (2 generation - Ex. 6:18). His sons - Mishael and Elzaphan (3 generation) helped Moses in the sanctuary (Lev.10:4). However, as only Caleb the son of Jephunneh, and Joshua the son of Nun remained alive after 40 years in the desert (Num.26:64,65), in the promised land not Mishael and Elzaphan came, but their sons (4 generation).

Phallu (1 generation) begat Eliab (2 generation). Eliab begat Dathan and Abiram (3 generation), who had supported Korah’s revolt in the desert. They did not come to the promised land, but their sons did (4 generation).

Zerah (1 generation) begat  Zabdi (2 generation), Zabdi begat Carmi (3 generation). Carmi begat Achar (4 generation), who came to the promised land (Joshua 7:18).

Some people came to the promised land in the fifth generation: 
Hezron- Ram-Amminadab-Nahshon- Nahshon’s children; some of them even in sixth generation- Hezron - Caleb - Hur -Uri- Bezaleel –(1Chron.2:18-20; Ex.35:30), but nobody - in third. 

There in the Bible in details only one bloodline is given, it is  the line Levi-Kohath-Amram-Moses, therefore we can assume, what this bloodline is given as an example for the counting of  generations.

Hence, the Jews were in Egypt for 215 years and came to the promised land in the fourth generation.