"Therefore know that the LORD your God, He is God, the faithful God who keeps covenant and mercy for a thousand generations with those who love Him and keep His commandments; and He repays those who hate Him to their face, to destroy them. He will not be slack with him who hates Him; He will repay him to his face. Therefore you shall keep the commandment, the statutes, and the judgments which I command you today, to observe them." (vv.9-11)
Israel was holy in their standing before God before they were holy in their conduct. They were set apart unto God by His choosing (God has chosen you to be a people for Himself) and were then called to live as chosen people. Their election meant the LORD set His love on them which became their motivation for total obedience. It took 40 years of wondering in the desert but when they really believed God loved them, and began living with that belief as a conscious fact, they (and we) found it so much easier to obey – and to utterly destroy anything that would damage that relationship of love.
Over many generations the Canaanites had demonstrated their hatred for God. Now, using Israel as His instrument, God will repay them with judgment. Their recollection of God’s faithfulness to them in the past would give them hope for their struggles ahead. God's promised He would go before Israel and fight for them (the great and awesome God, is among you), but He would not drive all the enemies out at once.
However, the LORD their God would drive out those nations before them little by little; you will be unable to destroy them at once, lest the beasts of the field become too numerous for you.
Sometimes to our frustration, this is the way God often works in our life. He clears things away little by little even though we might prefer it all at once. But, just as God wanted Israel to grow spiritually in the process of taking the Promised Land, so He wants to grow spiritually as we walk in faith with Him as well.
The Truth: "We walk by faith, not by sight." (2 Corinthians 5:7)