Albert Barnes Commentary Psalms 139:4

"For there is not a word in my tongue, But, lo, O Jehovah, thou knowest it altogether." — Psalms 139:4 (ASV)

For there is not a word in my tongue — All that I say; all that I have power to say; all that I am disposed at any time to say.

But lo, O Lord, you know it altogether — All that pertains to it. What is said, and what is meant. Merely to hear what is spoken does not necessarily imply a full knowledge of what is said — for it may be false, insincere, or hypocritical. God knows exactly what is said and what is meant.