HBO comedian Bill Maher often complains that the God of the Bible is a very jealous person. Why is God so jealous? Norman Geisler explains,
“God is jealous in the good sense of the word, namely, He is jealous for the love and devotion of His people (Ex 20:5). Paul spoke of a “godly jealousy” (2 Cor 11:2). The verses on God’s jealousy are all in the context of idolatry. Like any true lover, God is jealous when anyone or anything else steals the devotion of His beloved.
Human jealousy is often covering what does not belong to us. However, God’s jealousy is protecting what does belong to Him, namely His own supremacy. It is not a sin for God to claim allegiance of His creatures because He is the Creator. And He knows that it is best for them not to make an ultimate commitment to what is less than ultimate (idols). Only an ultimate commitment to what is really Ultimate will ultimately satisfy the human heart. God is jealous to protect this.”
That explains it all. God is jealous because we are His property, we are His creatures, we are His children and we belong to Him. Like a mother who wants best for her children, God wants best for us. When we settle for idols, we are missing His best. Lord Jesus had to turn away the money exchangers from the Temple premises. In the temple, they were supposed to worship one true God. But, they settled for money. Lord Jesus wanted us to worship God alone because He alone can satisfy our deepest longings.