Albert Barnes Commentary Psalms 119:172

"Let my tongue sing of thy word; For all thy commandments are righteousness." — Psalms 119:172 (ASV)

My tongue shall speak of your word — It shall speak of it in the language of praise; it shall speak of it in making it known to others.

For all your commandments are righteousness — I see this; I feel it; and, therefore, I will speak of it. My impression that your commandments are all righteous is so deep, that I cannot but speak of them. I must vindicate them; I must praise you for them.