She made him sleep on her knees; and she called for a man, and shaved off the seven locks of his head; and she began to afflict him, and his strength went from him.
The reason Samson lost his strength was only secondarily that he allowed Delilah to cut his hair. The real reason was that "the Lord had departed from him" (Judges 16:20). When God’s Spirit departed from someone under the Old Covenant, the results were disastrous (cf. 1 Samuel 16:14; Psalms 51:11).