Albert Barnes Commentary Psalms 71:15

"My mouth shall tell of thy righteousness, [And] of thy salvation all the day; For I know not the numbers [thereof]." — Psalms 71:15 (ASV)

My mouth shall show forth thy righteousness ... - See the notes at (Psalms 71:8). The word “righteousness” here refers to the righteous character of God, particularly as manifested on his behalf; the word “salvation” refers to what God had done to deliver him from his dangers.

For I know not the numbers thereof - That is, I cannot estimate the amount of your favors; they are innumerable. See the notes at (Psalms 40:5).