I understand the concept of war, even spiritual warfare, but I can say that I have truly missed understood why war matters. When Joshua went to war against the people of Canaan, the people experienced and learned that real power was not in the multitude or in the bravery or in the skill of its fighting men. It was solely in the might of God. The tapping into that might, and the possession of that power only took place when they were faithful to Him. Once Joshua left the scene, here is what they faced.
So then, the Lord left some nations in the land to test the Israelites who had not been through the wars in Canaan. He did this only in order to teach each generation of Israelites about war, especially those who had never been in battle before. They were to be a test for Israel, to find out whether or not the Israelites would obey the commands that the Lord had given their ancestors through Moses. – Judges 3:1-2,4 GNT
There was a generation that did not understand war and the only way for them to understand it was for them to experience it. Necessity teaches me to pray. There was distress in the land with these foreign nations still living among them and God used that in order to bring them back to focussing on Him. If anyone is going to learn to war then at the same time they would be learning to keep the commandments of God. Both were necessary. Blessings come when I listen to the voice of the Lord. Conflicts come to purify my soul and to ensure the kingdom of God is shared and is growing here on earth.
We have three needs – the need for wisdom to know our own hearts and Savior Christ better… the need for watchfulness to even die rather than yield one step to sin… and the need to be ever at war. Not to acknowledge this is the height of madness. We are to be killing sin or sin will be killing us. Owen offers his readers the big picture – he was not merely interested in seeing the believer abstain from a particular sin (or sins); for him, the whole goal of the Christian life was one of Christlikeness, which is only possible by intimately knowing Christ as He is revealed in the gospel.
To mortify a sin is not to utterly kill, root it out, and destroy it, that it should have no more hold at all nor residence in our hearts. It is true this is that which is aimed at, but this is not (in this life) to be accomplished. There is no man that truly sets himself to mortify any sin, but he aims at, intends, desires its utter destruction, that it should leave neither root nor fruit in the heart or life. He would so kill it that it should never move nor stir any more, cry or call, seduce or tempt, to eternity. Its complete eradication is the thing aimed at. Though there may be a wonderful success and eminency of victory against any particular sin, so that a man may have almost constant triumph over it, yet an utter killing and destruct- tion of it, that it should no longer exist, is not a possible condition in this life – as such, we are to “fight to the end!” This Paul assures us of: “Not as though I had already attained, either were already perfect” (Phil 3:12). He was a choice saint, a pattern for believers in faith and love and all the fruits of the Spirit, yet he had not “attained,” nor was he “perfect” (v. 15), but was “following after” – he still had a vile body like we have, that will be fully changed by the great power of Christ on the last day (v. 21). – John Owen