Judges 16:17

There hath not come a razor upon my head Though we have no account of it before, yet it seems from this, that it had been revealed by God to Samson, either by a dream or in some other manner, that his supernatural strength should continue as long as he continued in a Nazarite state, and did not suffer a razor to come upon his head to take off his hair. If I be shaven Not that his hair was in itself the cause of his strength, but because it was the chief condition of that covenant whereby God was pleased to engage to fit him for and assist him in that great work to which he had called him. But upon his violation of the condition, God justly withdraws his help.