Fear not: thou shalt not die - Here the discovery is made by God himself: Gideon is not curiously prying into forbidden mysteries, therefore he shall not die.

And the Lord said unto him,.... Either by a secret impulse upon his spirit, or by a voice from heaven; and even, as Kimchi observes, the angel, after he ascended, might cause this voice to be heard, seeing him in great fear, because he knew he was an angel; and which is another proof of this angel being Jehovah himself, the eternal Word:
peace be unto thee, fear not, thou shall not die; let not thy mind be ruffled and disturbed, but serene and calm; fear not that any evil shall befall thee, and particularly death; thou shall be safe from any danger whatever, and especially from death, which he expected in his flight would immediately follow.

Said unto him - Perhaps by an audible voice. Peace be to thee - Thou shalt receive no hurt by this vision; but only peace, that is, all the blessings needful for thy own happiness, and for the present work.