What does Judges 16:20 mean?

Samson made the foolish choice to trust Delilah, a woman he was not married to and was sleeping with in violation of several of the Lord's commands to Israel (Judges 16:5–6). His desires blinded him, spiritually, to the dangers of his foolish decisions (Judges 16:5–6). They led him to be manipulated and tricked (Judges 16:15–17). Now, after crossing so many moral lines during his life, the Lord will no longer empower Samson. His desires will blind him physically and permanently (Judges 19:21).

Under intense emotional pressure, Samson finally gave in to the woman he loved. Thinking she also loved him, he told her the secret of his power was in never cutting his hair. As soon as she had that secret, Delilah took advantage and prepared an ambush, shaving his head while he slept (Judges 16:18–19).

There was nothing special about Samson's hair, itself. It was just hair. Nazirite vows included several requirements (Numbers 6:1–21). The only one explicitly given to Samson for his entire life was that he never cut his hair. That was a visible sign of Samson's submission to God. The true source of his supernatural strength was the Spirit of the Lord. That power had been given directly by God so Samson could accomplish a mission for God (Judges 13:5). Delilah is certainly guilty for skillfully manipulating Samson's emotions. Yet Samson has been guilty of far more, by not being faithful to the Lord who called him for a special purpose. Telling Delilah his secret was not much different than shaving his own head; Samson betrayed his God-given purpose for the sake of a sinful desire. He loses his strength for that sin, not because the physical hair was detached.

For the final time, Delilah wakes Samson by calling out the same warning she's used before (Judges 16:9, 12, 14). Each time, Samson probably thought it was part of a game—so he'd wake up and easily break out of the bonds. Once again, he hears her words, and wakes up—not realizing his head is bare, and his superhuman power is gone.