It doesn't always make sense to me.
17 Perhaps you will think to yourselves, 'How can we ever conquer these nations that are so much more powerful than we are?' 18 But don't be afraid of them! Just remember what the LORD your God did to Pharaoh and to all the land of Egypt.
19 Remember the great terrors the LORD your God sent against them. You saw it all with your own eyes! And remember the miraculous signs and wonders, and the strong hand and powerful arm with which He brought you out of Egypt. The LORD your God will use this same power against all the people you fear. 20 And then the LORD your God will send terror to drive out the few survivors still hiding from you! 21 "No, do not be afraid of those nations, for the LORD your God is among you, and He is a great and awesome God.
Through all the difficult times that Israel has had to endure, I bet they never looked at their circumstances and thought to themselves that they were being prepared for God's mission. They couldn't see how they were a part of a really big plan that God had in motion.
God is judging the nations that Israel is being told to destroy, nations that had rejected the Lord and worshiped anything else that they could find instead of the living God, the time for mercy was over (Deut 9:4-5). The Israelites didn't have the right to show mercy to these nations that God was judging by signing a treaty with these people that would forfeit God's will (Deut 7:16).
You have the Lord and he is great and awesome, why should you be afraid to do the Lord's will? Didn't you see the power that your God had? (Deut 7:17-19)
Remember the awesome things that God did to the Egyptians, how you were able to walk away from such a powerful nation and to receive gifts as you were on your way out. Remember how he fed you and gave you water, he kept your clothes and your feet from wearing out (Deut 8:3-4).
God displayed his power to them back in Egypt so that they would know for sure that God was in control and he has the power to accomplish his will. God sustained his people out in the wilderness so that they would be humbled and have their faith tested before they went to battle so that they could exercise their faith and know his ability to provide for their needs when the going gets tough.
Sometimes we go through things that we cannot comprehend, but there is a bigger picture than what we can see, thats the perspective that God is working from, he sees the whole picture and he has a plan that makes no sense to us.
No matter what happens I will trust you Lord for everything, even when things do not make sense I need to be faithful and know that you are in control and I am a part of your bigger picture.