Leviticus 17:7 And they shall no more sacrifice unto devils, after whom they have gone a whoring. This shall be a statute for ever unto them throughout their generations.
This is the command and prediction of the First Commandment: My people will no longer sacrifice unto devils. Using the faithful marriage imagery and the image of the jealous God, who has bound Himself by covenant to be faithful to His people as bride, the Lord reveals to us what we give up for God. The pagan gods that were actually behind the idols and altars were devils, or demons. All the pagan gods of the world are real beings, not imaginary figures.
It took a long time and much tragedy for Israel to learn the lesson to believe in and worship Yahweh, the One True God, alone. For centuries, Israel would worship the local pagan gods and sacrifice to demons in addition to the worship of God. They tried to live in two worlds at the same time. It must be God or Baal, God or Mammon.
This is our response to the goodness, grace, and gospel of God. We no longer sacrifice to demons, and when we see it for what it is we abhor it all for devotion to God alone. The temptations of the world, pleasure, money, and power are the demon-gods that are always around us. But we learn to respond by no longer sacrificing to devils.