Albert Barnes Commentary Judges 16:20

"And she said, The Philistines are upon thee, Samson. And he awoke out of his sleep, and said, I will go out as at other times, and shake myself free. But he knew not that Jehovah was departed from him." — Judges 16:20 (ASV)

The possession of his extraordinary strength is ascribed (for example, Judges 13:25) to the presence of the Spirit of the Lord. Now the Lord, or the Spirit of the Lord, had departed from him, and so his strength had gone too. The practical lesson against the presumption of self-dependence, and the all-importance of a hearty dependence upon God’s Holy Spirit, must not be overlooked.