This shall be a sign unto you. — The sign was not such in itself, but became so by its agreement with the prediction. It was something exceptional that a new-born infant should be found, not in a cradle, but in a manger; still stranger that that infant babe should be the heir of the House of David.
Related Commentaries of Luke 2:12
Luke 2:12
12 And this shall be a sign unto you; Ye shall find the babe wrapped in swaddling clothes, lying in a manger.