Leviticus 20:1-5

Now according to The Dictionary of Biblical Imagery: “Molech was the Canaanite deity to whom Israel, in times of apostasy, sacrificed children. Molech appears approximately fifteen times in the Old Testament, and is a striking image of what the Bible finds utterly abominable in idolatry. Israel is explicitly commanded not to give any children to be sacrificed to Molech. The penalty for this behavior is to be “cut off” from Israel. No contempt is spared for Molech, who is called “the detestable god of the Ammonites.”

And in Josiah's reform at Jerusalem, the places in the Valley of Ben Hinnom where Israel had sacrificed their sons and daughters to Molech are desecrated. It is this grisly image of a god who devours sons and daughters, the dearest things in life, which is most memorable.”

Leviticus 20:2-5

Molech was well known as a god who demanded human sacrifice and so God says "I don't want you people to have anything to do with that kind of worship. It's not right." And He used some pretty strong language there about how He is going to deal with people who do that sort of thing. This was the kind of thing that Abraham would have known was wrong.

Leviticus 20:1-5

This is, I believe, the first place in the Bible that idol worship is directly associated with harlotry. God makes a very clear distinction, a contrast, between His way and the heathen's way. Right in this same section (we won't read the whole thing) He calls occultism harlotry.