Covenants between two people are typically witnessed by a third party. If one person doesn’t live up to his obligations and tries to argue that it was not necessary, the other person can then appeal to the witness to confirm the original terms of the agreement. Moses calls on the sky and the land to be the witnesses here. They will always be around to testify about the covenant terms that were offered to the people and how they agreed to them.

The formal treaty and its supplement have now been drawn up and witnessed. The only business remaining is to establish how the treaty will be carried on once the people who originally made it are gone. The Lord chooses Joshua to succeed Moses, to lead Israel into the land and represent them in their relationship with Him.