He shall eat curds and honey when he knows how to refuse the evil and choose the good.
15. Butter and honey shall he eat. Here the Prophet proves the true human nature of Christ; for it was altogether incredible that he who was God should be born of a virgin. Such a prodigy was revolting to the ordinary judgment of men.
Here, I. God, by the prophet, makes a gracious offer to Ahaz, to confirm the foregoing predictions, and his faith in them, by such sign or miracle as he should choose (Isa 7:10, Isa 7:11): Ask thee a sign of the Lord thy God; See here the divine faithfulness and veracity. God tells us nothing but what he is able and ready to prove.
Commenting on Isaiah 7:10-16
Butter and honey shall he eat..... As the Messiah Jesus no doubt did; since he was born in a land flowing with milk and honey, and in a time of plenty, being a time of general peace; so that this phrase points at the place where, and the time when, the Messiah should be born, as well as expresses the truth of his human nature...