Romans 3:25
Everyone loves a loving God. But when you begin to talk about God's wrath, God's jealously, the carpet and the conversation over there (anyone but this one) becomes more interesting. Why? Because no one really likes the idea of an all-powerful God on the rampage.
Now, the term "rampage" is certainly utilized here more for it's abrasive nature than for it's theological merit, but it is a close definition of God's feelings about sin. The reality is that God not only dislikes sin, but his feelings take on a more active nature. The jealously and wrath of God are uncomfortable, but essential concepts for every Christian.
The jealously of God (Ex. 20:5; Is. 48:11) simply means that God will have no other God's (or anything else) receiving worship in His place. Idolatry, simply defined, is spiritual adultery. And God's desire to restore us to proper worship of Him is very active, and His desire to be the only object of our worship is supreme.
The wrath of God (Ex. 32:9-10; Deut. 9:7-8; John 3:36; Romans 1:18) is God's reaction to sin. He doesn't just dislike it, He actively hates it! And God's wrath is Him actively seeking to punish sinners.
"Propitiation" is a term which, to a Christian, pertains to Christ. In this Christian understanding, Christ was the propitiation for our sins, meaning that he received the full wrath of God, those actions dictated by the jealously of God, for us. This is why the understanding of the wrath of God and the jealously of God are essential for every Christian, because without them, there was no need for Christ to die on the cross, and thusly no need for salvation.