In our text, Joshua was now taking over the leadership of Israel after the long ministry of Moses. He could have been easily overwhelmed if all he did was evaluate himself and his new position based upon the past ministry of Moses.
But God points Joshua to the only one who had the right to judge, the One who placed him in his new position, God Himself. And He left Joshua with a promise, “I was with Moses, so I will be with you. I will not leave you or forsake you.”