The hair is a sign, not a supply. Judges says where the strength came from on three separate occasions before Delilah ever appears, and each time the answer is the same and it is not a haircut.
The vow had three terms and only one of them is famous
Samson was put under a Nazirite vow before he was born, and the angel’s promise about him is smaller than people remember. He shall begin to deliver Israel out of the hand of the Philistines, says Judges 13:5. Begin. Nobody was ever told he would finish it. Numbers 6 sets out what that meant, and it is a list of three.
No wine, and nothing from the vine at all, down to the skins and the seeds. No razor. And no contact with a dead body, which Numbers 6:7 presses hard, ruling out his father, his mother, a brother and a sister alike, when they die.
The hair is the visible one. A man keeping the first and third restrictions looks like everybody else; a man with uncut hair can be identified across a field. Numbers 6:7 calls the hair the consecration of his God upon his head, which the New International Version and the New Living Translation render symbol and the Common English Bible renders sign, and says not a word about what it does for him.
Judges names the source three times
Before the Delilah story, every feat Samson performs is explained the same way, and the explanation is not his head.
He tears a lion apart, and the verse says the Spirit of the LORD came mightily upon him. He kills thirty men at Ashkelon, and the verse says the Spirit of the LORD came upon him. He breaks the cords at Lehi, and the verse says the Spirit of the LORD came mightily upon him and the ropes became as burnt flax.
Three feats, three attributions, no hair in any of them.
Samson is the one who says it
He tells her all his heart, says the verse, and then:
There hath not come a razor upon mine head; for I have been a Nazarite unto God from my mother’s womb: if I be shaven, then my strength will go from me, and I shall become weak, and be like any other man.
Judges 16:17 (KJV)
This is the sentence the picture is built on, so be exact about what it is. It is Samson speaking, not the narrator and not God, and he does not say the hair is the engine. He says he has been a Nazirite from the womb, and then that shaving will cost him. The hair is the terms of an arrangement he is about to break.
One verb does all the departing
Here is the thing that settles it, and it is visible to anybody with a text that carries the numbers.
The verb is sur, to turn aside or depart, and Judges uses it four times in this story. The first time the subject is Samson himself. He turned aside to see the carcase of the lion, says 14:8, and that is the first breach of the vow the book records. Then twice for the strength: in 16:17 Samson tells her it will go from him, and in 16:19, when the shaving happens, the narrator says it went.
And then, one verse later, the same verb again.
And she said, The Philistines be upon thee, Samson. And he awoke out of his sleep, and said, I will go out as at other times before, and shake myself. And he wist not that the LORD was departed from him.
Judges 16:20 (KJV)
The LORD was departed. Same word, fourth time, and this time the subject is neither Samson nor his strength. Judges is telling you that the strength leaving and the LORD leaving are one event described twice, and it puts the two sentences one verse apart so you cannot miss it.
He wist not. The most frightening clause in the chapter is that he got up expecting to be himself.
A lesson about promises lets everybody off
When this story comes up I have used it to talk about keeping your word. That is a fine subject and it is not what Judges is doing. Samson had broken the vow in other places long before the haircut. He turned aside to a lion’s carcass and ate out of it, which the vow forbids, and told nobody. The hair was the last term still standing.
Reading it as a parable about discipline lets everybody in the room off, because we all keep some promises. Reading it as Judges wrote it does not, because the question stops being what Samson failed to maintain and becomes who had been holding him up.
And the hair is not even the thing he lost. Delilah calls in a barber while he sleeps on her knees, so the one term he had kept was taken from him by another hand, without his consent and without his knowledge. What he gave away himself was the information.
The end has no hair in it either
His hair grows back in 16:22, and the verse says only that. It does not say the strength returned with it, and no verse between there and the temple says so. The narrator plants that line where he plants it for a reason, and what follows it is not another feat.
And Samson called unto the LORD, and said, O Lord GOD, remember me, I pray thee, and strengthen me, I pray thee, only this once, O God, that I may be at once avenged of the Philistines for my two eyes.
Judges 16:28 (KJV)
Strengthen me. He asks God, at the end, in as many words, and his hair does not come into it. Whatever he had, he had never owned, which is the same discovery the disciples made when they worked out that nobody gets in on his own resources.
Judges puts the verb in four places and trusts somebody to count them. Nobody in the chapter says the strength was in the hair, and nobody says it was not; the book simply puts the two departures a verse apart and moves on to the mill.