"And the Lord said, 'Now get up and cross the Zered Valley.' So we crossed the valley. Thirty-eight years passed from the time we left Kadesh Barnea until we crossed the Zered Valley. By then, that entire generation of fighting men had perished from the camp, as the Lord had sworn to them. The Lord's hand was against them until he had completely eliminated them from the camp." NIV translation
The Zered Valley surrounds a stream that flows from the east and goes into the southern end of the Dead Sea. This was the border between the lands of Edom and Moab.
The Israelites had wandered around for thirty-eight years so that all of those fighting men who had not trusted in the Lord would perish. At that time, God called Israel to cross the valley and to continue on their trip to the promised land.
That is a reminder to us that it is only by faith that we can enter into the promised land. That promised land is walking with God on this earth as we wait for the coming new heaven and new earth.
"Now when the last of these fighting men among the people had died, the Lord said to me, 'Today you are to pass by the region of Moab at Ar. When you come to the Ammonites, do not harass them or provoke them to war, for I will not give you possession of any land belonging to the Ammonites. I have given it as a possession to the descendants of Lot.'" NIV translation
Once again, Moses reminds the people that they had passed through the land of their relatives the Ammonites. They had not fought there because it was not a part of their promised land. The Ammonites were relatives because they were descended from the relationship between Lot and his daughter.
"(That too was considered a land of the Rephaites, who used to live there; but the Ammonites called them Zamzummites. They were a people strong and numerous, and as tall as the Anakites. The Lord destroyed them from before the Ammonites, who drove them out and settled in their place." NIV translation
Moses reminds the people that God had cleared the land of its giants and given it as an inheritance to Lots' descendants. That is a reminder to us, as Christians, that we all have our different giants to face but God will handle them all.