“Do not gloat when your enemy falls; when they stumble, do not let your heart rejoice.” This is SO easy to do, and it’s so much a part of our culture, and our humanity. We do it in sports, school, business, and relationships, not to mention military action, which I don’t think the author is talking about. It’s pride and superiority, as well as a sense of revenge, that motivates us. And it’s just wrong.
David was a great example of this. He mourned at the death of Saul, even though Saul had tried to kill him over and over. Later he wailed at the death of his son, Absalom, who had just rebelled against him and chased him out of the city.
Mt. 7.2 (=Mk. 4.24) says: “…with the measure you use, it will be measured to you…” Don’t gloat over your enemy’s downfall, or you just may bring on your own. Instead, against all intuition and human advice, Romans 12.20-21 instructs us to quickly meet our enemy’s needs. God’s ways are opposite of man’s.