God loves us all.  He comes to save sinners. God “desires everyone to be saved and to come to the knowledge of the truth.” (1 Tim 2:4). So, rather than rejoicing when our enemies fall, we should feel sad that we are not able to prevent them from suffering destruction because of their folly. If we rejoice over the downfall of our enemies, it shows that we are vindictive. If we have true love like David and our Lord for our enemies, we will pray for them. We will do what we can to save them. And if we cannot, we commend them to the Lord as Jesus did on the cross. We rejoice only when the lost sheep is found.