Why did Moses pick Joshua and not another man to lead the people into the Promised Land?
Moses picked Joshua to lead the people into the Promised Land because God had picked Joshua. Moses was only doing what God had asked. Moses was not allowed to take the Jewish people into the Promised Land because he had disobeyed God in the Wilderness of Zin (Num. 20). Moses was disappointed and so he asked God for a second chance and God said no. Then God told Moses that Joshua would take the people into the Promised Land. Listen to God,
But commission Joshua and encourage and strengthen him, for he will lead this people across and he will cause them to inherit the land that you will see. Deuteronomy 3:28 (NIV)
We do not know all of the reasons why God selected Joshua. But we do know that Joshua was special. Joshua was one the leaders among the people who were selected to go and spy out the Promised Land. When they came back from their trip, only two of the twelve men believed that God would keep them safe. Joshua was one of those men. These events are recorded in Numbers 13-14. From this we know that he had a very strong trust in God. Were there other reasons? The Bible does not tell us. So God selected Joshua, and when it was time for the people to enter the Promised Land, Moses told the people that Joshua would lead them.
Then He commissioned Joshua the son of Nun, and said, “Be strong and courageous, for you shall bring the sons of Israel into the land which I swore to them, and I will be with you.” Deuteronomy 31:23 (NASB)