Joshua 12:6 "Moses, the servant of the Lord, and the people of Israel defeated them; and Moses the servant of the Lord gave their land for a possession to the Reubenites and the Gadites and the half-tribe of Manasseh."

The "they" who Moses and the people of Israel defeated were Shion, king of the Amorites, and Og, king of Bashan (Joshua 12:2, 12:4). Obviously, these were not the only kings the people of Israel defeated in order to take possession of the Promised Land, the Book of Joshua details each of those defeated peoples and kings turn, telling us whether it was Joshua or Moses who was leading the people in these battles.

Notice that each time Moses is referred to in this verse, he is called "servant of the Lord." The Book of Joshua even begins with "After the death of Moses the servant of the Lord..." (Joshua 1:1) Joshua is not referred to this way, even though he also was God's servant (see, for example, Joshua 12:7, "And these are the kings of the land whom Joshua and the people of Israel defeated...") Moses, then, is given special recognition as "the servant of the Lord" when he is referred to in the Book of Joshua.

The relationship between God and Moses was so close, there really was no other prophet like him, so I can see why the people would give him this special recognition, especially so soon after his death. I think, too, though, that God inspired this honorific for Moses in order to set him apart, to remind people always of His special relationship with Moses and how Moses uniquely served God with everything he had. Even though Moses did not get to enter the Promised Land because of his unfaithfulness in striking the rock at Meribah, God did not want him to be remembered for that. He wanted Moses to be remembered and honored as the faithful servant who did mighty, wonderful things for God and His people.

I find this a comforting reminder that once God forgives our sins and we have fully atoned for them, they are forgotten in His eyes. All He then sees is the good we have done. He will allow the memory of our good works be our legacy, not our sinfulness. We do have to acknowledge and pay the price for our sins (either here or in Purgatory), just as Moses did, but once we do that, our ledger is clean and God does not linger on our sin, nor allow it to be our legacy. 

We all, including Moses, still need the sacrifice of Jesus Christ to achieve salvation, but we will be fully ready to receive it when we repent and atone for our sin. Then we will be remembered as servants of the Lord, rather than for our sinfulness. God is so very good to us if only we accept what He offers us!