What does Psalm 139:7 mean?

If David wanted to escape from God's all-encompassing knowledge, he would not find any place to hide from God.

Elijah fled to the desert south of Judah to escape Jezebel's wrath, but he could not distance himself from the Lord. The Lord revealed Himself to Elijah in a low whisper and gave him new opportunities to serve Him (1 Kings 19:9–18).

Jonah tried to flee from God's presence when God commanded him to go to Nineveh and call out against it. Instead of going east to Nineveh, he boarded a ship headed west to Tarshish (Jonah 1:1–3). He soon discovered God was present, no matter how far he ran. The Lord prepared a great storm which led to Jonah being cast into the sea, and still God was there (Jonah 1:11–12). He had appointed a great fish to swallow Jonah (Jonah 1:17). In the belly of the fish, Jonah repented and vowed to obey the Lord (Jonah 2:1).

For an obedient believer, the omnipresence of God is a comfort. Jesus said, "And behold, I am with you always, to the end of the age" (Matthew 28:20). Hebrews 13:5 echoes the promise "I will never leave you nor forsake you." This promise means we do not have to fear what anyone can do to us (Hebrews 13:6).