for you shall not worship any other god, for the Lord, whose name is Jealous, is a jealous God.
— Exodus 34:14
What does it mean that God is a jealous God? When we use the word “jealous” in reference to other people, it almost always has a negative connotation, but not so with God. God is not jealous of us, He is not jealous of some other god, because there is no other god—merely figments of somebody’s imagination.
He is jealous for our good in the same way that every father and mother here is jealous for their children. Hopefully no one is jealous of them, but jealous for them, that they might have the best education, that they might eat the best food, that they might have the best care, that they might grow up to be the best people they possibly can be. And you are angry with anything that threatens the best for your children, anything that threatens to harm them.
That is why He commands us to “have no other gods before Me.” He knows that if we worship anything less than the true God, we will become like that which we worship and will therefore become far less than we could be.