To shew that the Lord is upright - That is, This will be a proof that God is faithful to his promises; that he is the true friend of his people. The fact that they live long - that they are happy and useful even in old age, will be a demonstration that God is the friend of virtue, and that he deals with people according to their character.
He is my rock - He is my defense; that which constitutes my security. See the notes at Psalms 18:2. This is language of strong confidence in view of all that is said in the psalm.
And there is no unrighteousness in him - This is said in the most absolute form - implying the most entire confidence. God is altogether to be trusted. There is no evil or wrong in his character or in his dealings. In all respects he is worthy of confidence: “worthy” to be loved, trusted, adored, obeyed, by the inhabitants of all worlds. What a sublime thought is this! What a consolatory truth! What would the universe be if God, a Being of infinite POWER, were not a Being of perfect RIGHTEOUSNESS, and could not be trusted by the creatures which he has made!