John Calvin on Joshua 23:6

6. Be you therefore very courageous, etc He now shows them the mode of conquering, — not to indulge gross security, as too often happens, as a substitute for genuine confidence. He affirms that God will be propitious to them, and promises that whatever they attempt will turn out prosperously, provided they are steadfast in obeying the Law. However confidently hypocrites may contemn and deride God, they would wish, however, to have him astricted to them; nay, they often, with no small pomposity, boast of his promises. But true faith, while it reclines upon God, keeps those who possess it in his fear. In short, those who would find God must seek him sincerely, and if we desire to be regarded by him, we must beware of turning our backs upon him. The expression, Be you very courageous, as has elsewhere been said, denotes serious study, because in the great weakness of our nature no man will set about the thorough observance of the Law, if he does not exert himself above his strength. Attention ought also to be paid to the definition of true obedience which is here repeated from Moses, (Deuteronomy 5:32) and said to consist in not turning either to the right hand or the left.