John Wesley on Deuteronomy 32:4

A rock - As for the stability of his nature, and invincibleness of his power, so also for his fixedness and immutability in his counsels and promises and ways; so that is there shall be a sad change in your affairs, remember that this proceeds from yourselves and from the change of your ways towards God, and not from God, in whom there is no variableness or shadow of change, Jam 1:17. His work - All his works and actions are unblameable, perfect, wise and righteous. His ways - All his administrations in the world and particularly with you are managed with wisdom and justice. A God of truth - Constant to his promises: you cannot accuse him of any unfaithfulness to this day.