Question: An atheist I know does not believe there is time for Judah to produce all his descendants given in Genesis 38 and 46 during the time that Joseph was sold into slavery in Egypt and was reunited with his brothers and father, Jacob.
Answer: Your atheist friend is wrong! There is time enough. Let me explain that Judah and Joseph are two of the twelve sons born to Jacob by his 4 wives: Leah, Rachel, and Bilhah and Zilpah, their handmaids. At the end of the first seven years of their marriage, we find Jacob’s wife, Leah, had born him six sons and a daughter. (Genesis 30:20,21). Judah was the fourth in birth order.
Judah would have been about 3 years old when Jacob’s eleventh son, Joseph, was born at the end of the seven years. Judah would have been approximately 20 years old when he and his brothers sold Joseph to the Ishmaelites at age 17, and, approximately 42 years old when Jacob and his sons and their families went down to Egypt to reunite with Joseph after 22 years there.
Scripture tells us that Joseph was 30 when he became Pharaoh's “second in command.” (Genesis 41:46). We add the 7 years of plenty (Genesis 41:53,43) and 2 years of famine (Genesis 45:10,11), making Joseph 39 years old when the family gets together. We subtract Joseph’s age of 17 when he went to Egypt (Genesis 37:2) from 39 and arrive at 22 years in Egypt.
Let us briefly recap the events of Genesis 38. Judah marries a Canaanite wife. Er, his firstborn, marries Tamar; but is wicked and is slain by the Lord. (Genesis 38:6,7). His second son was slain by the Lord for refusing to raise up seed to his brother with Tamar. (Genesis 38:9,10). Judah then sends Tamar to her father’s house and tells her to remain a widow. Tamar believes Judah is withholding the third son; and deceives Judah by impersonating a prostitute; and he conceives two more sons by her, Pharez and Zarah. (Genesis 38:25-30). Pharez is listed as having 2 sons in Genesis 46:12, making Judah a grandfather.
We know that Jacob’s sons married at a fairly young age, as they all had families when they went to Egypt; and two, Judah and Asher, had 2 grandchildren apiece. (Genesis 46:5-27).
The problem is not that Judah could not have had 2 grandchildren when he went down to Egypt; but, that your friend does not believe God’s Word.
“The entrance of thy words giveth light; it giveth understanding to the simple.”Psalm 119:130
“Study to shew thyself approved unto God, a workman that needeth not to be ashamed, rightly dividing the word of truth.” ‑ 2 Timothy 2:15