Now the Lord said to Joshua: "Do not be afraid, nor be dismayed; take all the people of war with you, and arise, go up to Ai. See, I have given into your hand the king of Ai, his people, his city, and his land.” Joshua 8:1
The Lord told Joshua to go up to Ai. Actually, He was telling Joshua to go back to Ai. Since their earlier defeat at Ai, the men of Israel have been through a tragic experience because of the disobedience of one of their men, Achan. The punishment for Achan's sin no doubt left a fearful impression upon all these men, who must now be prepared for war. So the Lord tells Joshua to "not be afraid, nor dismayed." In other words, He is saying, “Get back up and let's take care of the business at hand. Let's complete the job we have started.” The Lord promises to be with Joshua and his men, even going so far as to tell Joshua that He has already given the king, the people and the land into their hands.
In the second part of this verse, the Lord tells Joshua to "see." This is not a physical seeing because the battle has not yet even begun. This form of seeing requires spiritual eyes of faith to believe that what the Lord is saying is true, even though it cannot be physically seen at this time. For Joshua, this is an important step of faith. He has just been dealt a severe blow through what happened with Achan and now he must get back up. He must continue to fight. He must take each step with the Lord.
God is faithful and just. He will complete the work He has started. Do not let fear, anger or discouragement keep you from following the Lord. Get back up, trust Him and take that next step. The enemy will do whatever he can to keep you from taking that next step, but the Lord will help you to "see" that He has delivered you and will lead you forward.