I am wondering how all the nations came to be. If there were only two people in the beginning, how did they multiply and become different nationalities? The only way I see is through incest. Incest is a sin so I just don't get how the world is filled with people but started with only two. It doesn't make any sense.
You are correct that incest as we know it today is a sin. However in the beginning inbreeding wasn't. Your thought process is also correct of how the human race began. Intermarriage occurred back in the original days. God ordained this to be be. This was before the law prohibiting it came to be as stated in the book of Leviticus which reads;
"None of you shall approach to any that is near of kin to him...." Lev. 18:6
In the book of Genesis, it gives some of the original genealogy from Adam an Eve. Chapter four gives the descendants of Cain (Adam's son), then in chapter five it continues with the genealogy of Adam and his descendants. (which do not include Cain or Abel). This genealogy spanned hundreds of years, and eventually led to Noah and Abraham. As part of the covenant with Abraham, God had Abraham look at the amount of stars in the sky to see if he could count them and said, "So shall thy seed be".
As the people multiplied and were scattered throughout the land, God also initiated the different languages. We see this in His word;
"Come, let Us go down and there confuse their language, that they may not understand one another's
speech." So the LORD scattered them abroad from there over the face of all the earth, and they ceased
building the city. Gen. 11:7,8
This is the result of there being over several thousand languages and dialects today.
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