John Gill Commentary Psalms 71:22

"I will also praise thee with the psaltery, [Even] thy truth, O my God: Unto thee will I sing praises with the harp, O thou Holy One of Israel." — Psalms 71:22 (ASV)

I will also praise thee with the psaltery
An instrument of music; (See Gill on Psalms 33:2);

[even] your truth, O my God ;
that is, his faithfulness in fulfilling his promises, which is never suffered to fail;

unto you will I sing with the harp ;
another instrument of music; and both typical of the spiritual melody in the heart, which believers make in praising the Lord, when they sing the Lamb's new song; see (Revelation 14:2Revelation 14:3) ;

O you Holy One of Israel ;
the God of Israel, that dwells among them, and sanctifies them; and who is essentially and perfectly holy in himself, and in all his ways and works; the remembrance of which occasions praise and thankfulness, (Psalms 97:12) .