How can it be believed that the Messenger is the Creator, and that we must apply all that He has sent down?

The answer to the question is built upon the belief in the truthfulness of Muhammad (peace be upon him), for he is a messenger from God, and God has commanded us to believe in him and follow him. God clarifies to the Messenger that He is His sender by manifesting signs and miracles to him, such as Moses' staff turning into a snake, and the miracle of Al-Isra' wal-Mi'raj for Muhammad (peace be upon him).