By the time Israel entered the land of Canaan, the nations there had “run the full course”—they had surpassed the threshold of moral collapse, much like nations have done today. God knew that this would happen and had told Abram about it, over 400 years earlier: “And you shall go to your fathers in peace; you shall be buried in a good old age. But in the fourth generation they [Abram’s seed—the nation Israel] shall come here again: for the iniquity of the Amorites is not yet full” (Gen. 15:15-16).
Here, the word “iniquity” comes from the Hebrew word avon, which means “perversity, mischief or sin.” If there had been no law in force, there would not have been any iniquity or sin for the Amorites, or any other nation, to commit. Refer to Leviticus 18:3, 19-30 for more description of the iniquity and abominations committed by the Canaanites. They included sacrificing—murdering—their children in the fire of Molech, every form of adultery and sexual perversity, and profaning the name of God.
Take a look at the pre-Flood world: “And God saw that the wickedness of man was great in the earth, and that every imagination of the thoughts of his heart was only evil continually” (Gen. 6:1-3, 5-6). The word “wickedness” used here comes from the Hebrew word rah, which means “exceedingly evil.” So wicked was mankind that verse 6 tells us, “And it repented the Lord that He had made man on the earth, and it grieved Him at His heart.” This wickedness brought every conceivable type of sin and blatant disregard for the sanctity of life.
These sins were imputed—pointed out—by the laws of God—the Ten Commandments, which existed from the creation of mankind.
These examples show that all the Ten Commandments preceded Moses. From Adam to Moses, all men had sinned—had broken God’s laws, the Ten Commandments. That is why God commended Abraham, saying, “Abraham obeyed My voice, and kept My charge, My commandments, My statutes and My laws” (Gen. 26:5).
Abraham sacrificed to Melchizedek, and Noah also sacrificed after the ark landed, and they walked out on dry land. Noah knew that clean animals were to be used because he brought 7 couples of each clean animal into the ark before the flood.