In the Bible, my enemy is someone who does not like me, someone who wants to do me harm, never someone I don’t like or to whom I want to do harm. Jesus doesn’t allow us to be that way. In fact, He said we are to love our enemies and pray for those who persecute us (Mt 5:44).
So my enemy who falls in this verse is not someone I don’t like, but someone who doesn’t like me – and I am not supposed to be happy when they fall. There are many reasons why I shouldn’t, but this verse only mentions one. If I rejoice in his calamity, the LORD will know and He reserves the right to stop this process in my enemy’s life.
While this person is not right – or else they would not have an “enemy attitude” toward me – the LORD speaks to me about my attitude in this situation! If my attitude is not appropriate He says He will turn His wrath away from my enemy.
It is not that my enemy is going to get away with anything, it’s just that He is going to deal with them later in some other fashion, because my attitude got in the way during this process.