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 ) .