To shew that the LORD is upright: he is my rock, and there is no unrighteousness in him.
To show that the Lord is upright: (he is) my rock, and (there is) no unrighteousness in him - akin to Deuteronomy 32:4. "My rock" expresses God's stedfast faithfulness to His word. It in the second clause answers to "Yahweh" in the first, which name expresses unchanging faithfulness to His promises (cf. Psalms 92:2). God's uprightness, or straightforward, right dealing with His people, remains unchanged, even though for a time His people may seem to be forsaken.