When you will go out to war against your enemies, and God will deliver them into your hand, and you will capture its captivity.
This is what Rabbi Twerski writes about this verse:
Torah commentaries are unanimous in interpreting this verse as referring also to the internal war a person must serve against the yetzer hara.
The yetzer hara, evil inclination, is unfortunately something all of us must always fight against, a kind of constant battle. Besides in the month of Elul we are expected to be even more focused on our faults, regret them and strive not to repeat the same mistakes again.
Sadly as we grow up we also realize that we are continuously fighting the same battles and this may seem daunting and discouraging.
As if to make things worse, the first part of this line shows that our own willingness to engage in action must come first. No miracle will come from heaven, or elsewhere, unless we “go out to war”.
However the rest of this verse assures us that, as long as we are willing to defeat the yetzer hara in our lives, we are not alone: God will assist us. Progress is possible provided we make God an assistant in our efforts to be different and better people.