Deuteronomy 9:1-3 KJV
Hear, O Israel: Thou art to pass over Jordan this day, to go in to possess nations greater and mightier than thyself, cities great and fenced up to heaven,
A people great and tall, the children of the Anakims, whom thou knowest, and of whom thou hast heard say, Who can stand before the children of Anak!
Understand therefore this day, that the LORD thy God is he which goeth over before thee; as a consuming fire he shall destroy them, and he shall bring them down before thy face: so shalt thou drive them out, and destroy them quickly, as the LORD hath said unto thee.
I observe immediately that the book of Deuteronomy offers no possibility of Jewish defeat by the Canaanites. It is as if, before the first battle, the war has already been won. Judging from Rahab's response to Joshua's spies the conclusion of the war was already decided on both sides. The Canaanite understood they had no hope of winning this war.
In the light of this assurance, Israel was to understand that this was God's battle and God's doing. They were also to understand that the victory they would achieve was not because they deserved it but because the Canaanite's did not. Their victory would be an act of grace.
This is the foundational truth for outreach and evangelism today. Paul said that he (and by implication we) was a debtor. He did not deserve the grace he had received and therefore owed it to others to share that grace with them. Our place is to reach out to anyone and everyone that God enables us. Whether they respond positively and become saved or respond negatively and remain condemned is a matter entirely between them and God. The battle is the Lord's. We merely follow Him.