Psalms 71:22

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

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

unto thee 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 14:2 Revelation 14:3 ) ;

O thou 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 ) .