Commentaries:
There is heat in God's relationship with His people. Within the Ten Commandments, in the second commandment, He says, "For the LORD your God is a jealous God." What is jealousy? It is a passionate intolerance, even a hostility, toward a rival. It is also defined as vigilance in guarding a possession.
In this passage, God is having a passionate reaction against a rival, idolatry. God will not permit idolatry without reacting because idolatry promotes divided loyalties. We are His, and He does not choose to share us with anybody or anything else.
John W. Ritenbaugh
Prayer and Seeking God