Problem: In Galatians 3:17 Paul takes the 430 years of Exodus 12:40-41 to refer to the period from the day God appears to Abraham and he leaves for/into Canaan to the day of the Exodus. This is the most logical interpretation because Genesis 15:13 says his descendants will be “sojourners in a foreign land” for 400 years; Abraham is 75 when he leaves Haran (Gen. 12:4), and Isaac is born to him when he’s 100 (Gen. 21:5). This leaves us with 405 years technically, which is why some older commentators supposed that the 400 years began when Ishmael teased a 5-year-old Isaac (Gen. 20:9 – Ishmael laughed, presumably at Isaac’s expense). This is neither possible nor necessary to prove – 405 years can easily be rounded to 400 to carry the same sense, much like other ages and numbers are.
Solution: Moreover, the day God appeared to Abraham, causing him to leave Mesopotamia would’ve been much more important and memorable for both Abraham and the Israelites than the day Isaac was teased (even if it could have been noted as it was illegal that Hagar be thrown out). Exodus is clear that this was known to the day. The only other alternative would be the day of Isaac’s birth – certainly to be remembered by Abraham and Sarah their entire lives, especially in the moments Abraham had to walk him up to the sacrificial altar. But this would’ve been important mainly to Abraham and Isaac, and the day God appears to Abraham would’ve been infinitely more meaningful for everyone not just because man’s oblivion to false deities was over, but because it was this same deity who gave Abraham a son when his wife had been barren her entire life and had entered menopause altogether (Gen. 18:11). Throughout Scripture we see altars being made and dedicated whenever God appeared to the Israelites, so this is the better candidate and makes sense with the 400 vs 430 years as well as with Gal. 3:17.
It’s this 400 year value, which was the most familiar to both us and Paul’s audience in Acts 13:16-41 (cf. Acts 7:6) that gives us 450 in Acts 13:20. Paul adds to the 400, the 40 year Wilderness Wandering, and rounds it to ~450 with Joshua’s Conquest. Joshua’s Conquest took around 7 years. This is calculated from Caleb’s age. He says he’s 85 and that he was 40 when Moses sent him to spy from Kadesh-Barnea (Josh. 14:7, 10; Num. 13). The Israelites reached Kadesh-Barnea and sent spies 2 years after leaving Egypt (Deut. 2:14), which would make Caleb 38 at the Exodus, and 78 at its exactly 40 year end (Deut. 1:3). If we allow for rounding on Caleb’s part, we get 5-10 years for the Conquest, giving us 445-450 years from the “travellers in a foreign land” beginning with Abraham’s son Isaac (Gen. 15:13).
The reason why Exodus 12:40-41 tells us of 430 years “in Egypt” only is because Egypt was the focal point of the Exodus, the oppression, the fulfillment of making Abraham a “multitude”, and because Egypt was the foreign land – the Hebrews were oppressed here, despite being born here. Whereas, Isaac and Jacob were neither oppressed, nor foreigners to Canaan, being born there. Jacob even laments for Canaan and asks Joseph to bury him there and not Egypt or Haran/Ur. So it would have been quite awkward and unnatural to refer to the “foreign land” of Abraham’s promise as Egypt and Canaan in Exodus 12:40-41, especially since the Israelite were going to this “foreign” land! This would’ve been a natural designation for Abraham in Genesis 15:13, but not for Moses and the Israelites, but logically the 430 years extended over Canaan and the Septuagint attests this by amending the text to “430 years in Egypt and Canaan,” thus exercising one of its many attempts at reconciling the text.
