For the word of the Lord is right - The command; the law; the promise of God. Whatever he “says” is right; or, is true. It is worthy of universal belief; and should, therefore, be a reason for praise. The fact that God says a thing is the highest proof that it is true.
And all his works are done in truth - Or rather, “in faithfulness.” That is, All that he does is executed faithfully. He does all that he promises, and all that he does is such as to claim universal confidence. Whatever he does is, from the very fact that He does it, worthy of the confidence of all his creatures. None, however they may be affected by what he does, have any reason to doubt that it is perfectly right. God is the only Being of whom we have any knowledge, concerning whom we can feel this certain assurance.