John Wesley on Leviticus 18:21

Pass through fire - This was done, either by burning them in the fire, or by making them pass between two great fires, which was a kind of consecration of them to that God. Moloch - Called also Milcom, was an idol chiefly of the Ammonites. He seems to be the Saturn of the heathens, to whom especially children and men were sacrificed. This is mentioned, because the neighbours of Israel were most infected with this idolatry, and therefore they are particularly cautioned against it, though under this one instance all other idols and acts, or kinds of idolatry, are manifestly comprehended and forbidden.