Albert Barnes Commentary Psalms 139:6

"[Such] knowledge is too wonderful for me; It is high, I cannot attain unto it." — Psalms 139:6 (ASV)

Such knowledge is too wonderful for me - literally, “Wonderful knowledge away from me,” or, more than I can comprehend. It is beyond my reach; it surpasses all my powers to comprehend it.

It is high, I cannot attain unto it - It is so exalted that I cannot grasp it; I cannot understand how it can be.