John Gill Commentary Judges 6:23

"And Jehovah said unto him, Peace be unto thee; fear not: thou shalt not die." — Judges 6:23 (ASV)

And the Lord said to 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 to you, fear not, you will not die ;
let not your mind be ruffled and disturbed, but serene and calm; fear not that any evil shall befall you, and particularly death; you will be safe from any danger whatever, and especially from death, which he expected in his flight would immediately follow.