John Calvin Commentary Joshua 1:9

"Have not I commanded thee? Be strong and of good courage; be not affrighted, neither be thou dismayed: for Jehovah thy God is with thee whithersoever thou goest." — Joshua 1:9 (ASV)

Have not I commanded, etc. Although in Hebrew a simple affirmation is often made in the form of a question, and this phraseology is of very frequent occurrence, here, however, the question is emphatic, to give an attestation to what had previously been taught, while the Lord, by bringing his own authority distinctly forward, relieves his servant from care and hesitancy.

He asks, Is it not I who have commanded you? I too will be present with you. Observe the emphasis: since it is not lawful to resist his command.

This passage also teaches that nothing is more effective to produce confidence than when, trusting to the call and the command of God and feeling fully assured of it in our own conscience, we follow wherever he is pleased to lead.