John Gill 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
Expressed by it or upon it, just ready to be spoken; or, as the Targum, ``when there is no word in my tongue:'' so Aben Ezra, ``before it was perfect in my tongue:'' before it is formed there; while it is in the mind, and not expressed, and even before that;

[but], lo, O Lord, you know it altogether ;
the whole of it, from which it springs; the reason of it, what is designed, or the ends to be answered by it. The Lord knows the good words of his people, which they speak to him in prayer, even before and while they are speaking them; and what they say to one another in private conversation, (Isaiah 65:24) (Malachi 3:16) . See an instance of words known by Christ before spoken, in (Luke 19:31Luke 19:33) .