The hair of his head began to grow again - And may we not suppose that, sensible of his sin and folly, he renewed his Nazir vow to the Lord, in consequence of which his supernatural strength was again restored?

Howbeit the hair of his head began to (l) grow again after he was shaven.
(l) Yet he did not regain his strength, till he had called on God and reconciled himself.

Howbeit, the hair of his head began to grow again after he was shaven. It began to grow immediately no doubt, as it naturally would do; but it is highly probable it grew in an extraordinary manner, and in a short time became as when it was shaved (n), as it may be rendered, and upon which his strength was renewed; not that his strength naturally lay in his hair, and so naturally increased as that grew; but he being made sensible of his sin, and repenting of it, renewed his Nazariteship, of which letting his hair grow was a token; and it pleased God, who accepted of his repentance as genuine, of his own good will and pleasure to renew his strength; particularly upon his prayer to him, after related.
(n) "ut rasus fuerat", Tigurine version, Vatablus; "ut quum abraderetur", Junius & Tremellius.

Samson's afflictions were the means of bringing him to deep repentance. By the loss of his bodily sight the eyes of his understanding were opened; and by depriving him of bodily strength, the Lord was pleased to renew his spiritual strength. The Lord permits some few to wander wide and sink deep, yet he recovers them at last, and marking his displeasure at sin in their severe temporal sufferings, preserves them from sinking into the pit of destruction. Hypocrites may abuse these examples, and infidels mock at them, but true Christians will thereby be rendered more humble, watchful, and circumspect; more simple in their dependence on the Lord, more fervent in prayer to be kept from falling, and in praise for being preserved; and, if they fall, they will be kept from sinking into despair.

Howbeit the hair of his head began to grow again--It is probable that he had now reflected on his folly; and becoming a sincere penitent, renewed his Nazarite vow. "His hair grew together with his repentance, and his strength with his hairs" [BISHOP HALL].

Samson's Misery, and His Triumph in Death. - Judges 16:22. The hair of his head began to grow, as he was shaven. In the word כּאשׁר, as (from the time when he was shaven), there is an indication that Samson only remained in his ignominious captivity till his hair began to grow again, i.e., visibly to grow. What follows agrees with this.

The hair - This circumstance, though in itself inconsiderable, is noted as a sign of the recovery of God's favour, and his former strength, in some degree, upon his repentance, and renewing his vow with God, which was allowed for Nazarites to do.