At the end of Numbers 33, I read, “But if you do not drive out the inhabitants of the land from before you, then those you let remain of them will be as pricks in your eyes and as thorns in your sides, and they will harass you in the land in which you dwell. It shall happen that as I thought to do to them, so will I do to you.”
God does not give commands that cannot be kept. He does not warn without empowering.
The inhabitants of the land represent flesh/sin. In another place, God tells the Israelites that he will drive out the Canaanites slowly (but steadily) so that the land is not emptied and does not become filled with wild beasts (Ex. 23:29-30).
The thorns and wild beasts, in my opinion, represent a haughty spirit and condemning eye. It is a journey to overthrow sin completely. You can read that journey in 2 Peter 1:5-7. Yes, we should stop sinning immediately (1 Cor. 15:34), though “we all stumble in many ways” (James 3:2). If, however, you think you have already addressed all sin in your life, you have more revelation to come. God has you start by driving out the giants–lust, theft, drunkenness, jealousy, bitterness, your insulting tongue, etc.–but he will spend your life weeding out the smallest inhabitants: self-confidence, inconsideration, lack of hope. Your most minor grudges and offenses must be replaced with thanksgiving. This is the work of a lifetime.
Non-Christians (and some Christians, I suppose) have this concept of an “old soul.” An “old soul” has weariness in his (or her) eyes, but an old soul is no threat. He is safe, except to evil, which he chases away with wisdom and goodness, not wrath. The true old soul is not one that has lived many lives, as practitioners of eastern religions suppose, but one who has lived one life well. He is weary, but he stirs himself to love and serve. The weariness is from the toil and work of driving out the inhabitants of the land, of the flesh, and what is left is the handiwork of God.
“If these things are in you and increasing, they make you so you are neither barren nor unfruitful in the knowledge of our Lord Jesus Christ, but he that lacks these things is short-sighted, and cannot see far off, and has forgotten that he was purged of his old sins” (2 Pet. 1:8-9).
Cooperate with God in the process of clearing the land, little by little. At the end, you want to be fruitful, with many children, not blind, having forgotten the deliverance wrought in you from the beginning.