God describes idolatry as harlotry, playing around with someone else's spouse. It is a case of divided loyalties. God becomes angry, jealous, when this happens spiritually. In fact, in Deuteronomy 4:24, His anger becomes so hot that He describes Himself as being a consuming fire. Fire symbolizes God's radiant glory as an aspect of His holiness.
Zeal and jealousy are opposite sides of the same coin; both of them are driven by passion. One is positive, the other negative. One is for, one is against. Zeal is passionately for something or somebody, while jealousy is passionately against something or somebody. Similarly, fire is hot, and it is both positive and negative. It symbolizes both refining and purifying, on the one hand, and death and destruction on the other.
The pattern is in the way God depicts His feelings toward us. As a consuming fire, He will either purify or destroy with His passion. He is either for something with a great deal of ardor, or He is against something with a great deal of fury. He is for those who are with Him, and He is loyal to the nth degree to them. But He is against sin and disloyalty with just as much heat as He is for those who love Him and diligently seek Him. His attitude is not cool in any way, shape, or form, but hot. He wants us to respond in like manner.
In what way are we seeking God? Diligently? Earnestly? Sincerely? With warmth, ardor, and affection? Is our seeking the ardent pursuit of one in love—one who wants to be around this personality and really desires to know Him because we are, after all, going to marry Him and spend all eternity with Him? Or is it a kind of a take-it-or-leave-it, distant, academic coolness because we do not want to make a fool of ourselves or offend others with our zeal? Think about it.