Albert Barnes Commentary Psalms 119:138

"Thou hast commanded thy testimonies in righteousness And very faithfulness." — Psalms 119:138 (ASV)

Your testimonies that you have commanded - Your law, considered as a testimony as to what is right and best.

Are righteous and very faithful - Margin, as in Hebrew, "righteousness and faithfulness." They are so righteous, and so deserving of confidence—so certain to be accomplished, and so worthy to be trusted in—that they may be spoken of as righteousness and fidelity of the most perfect kind; the very essence of that which is right.