For the word of the LORD is right; and all his works are done in truth.
The first part (Psalms 33:4-16) of the main body; reasons why God is so to be praised (Psalms 33:1) - namely, for His truth, righteousness, creating, sustaining, and all-controlling power. Foremost stands His truth, or faithfulness to His promises. The Scripture promises existing in David's day were, even then, the comfort of the people of God.
The word ... right - rather, "upright," as the Hebrew is translated in Psalms 33:1. "The word of the Lord" is His promise to His people (Psalms 105:42).
And all his works are done in truth - or 'faithfulness.' "His works" answer in parallelism to His "word." His word and His works coincide. What He promises He performs (Numbers 23:19). His works are the result of His word (Psalms 33:9).