Gideon's naming the altar which he built, in commemoration of the words of peace spoken by the Angel, is very similar to what we read of Abraham Genesis 22:14, and of Moses (Exodus 17:15, when he named the altar Jehovah-nissi).

Gideon built an altar - and called it Jehovah-shalom - The words יהוה שלום Yehovah shalom signify The Lord is my peace, or The peace of Jehovah; and this name he gave the altar, in reference to what God had said, Judges 6:23, Peace be unto thee, שלום לך shalom lecha, "Peace to thee;" which implied, not only a wish, but a prediction of the prosperous issue of the enterprise in which he was about to engage. It is likely that this is the altar which is mentioned in Judges 6:26, and is spoken of here merely by anticipation.

Then Gideon built an altar there unto the Lord,.... On the top of the rock where he had laid his provisions, and which had been consumed by fire issuing out of it, as a token of divine acceptance, and as an assurance of his destroying the Midianites as easily and quickly as the fire had consumed them, and therefore had great encouragement to erect an altar here for God:
and called it Jehovahshalom; the Lord is peace, the author and giver of peace, temporal, spiritual, and eternal; so Jarchi,"the Lord is our peace,''a fit name for the angel that appeared to him, who was no other than the man of peace; who is our peace, the author of peace between God and man. This name he gave the altar, with respect to the words of comfort said to him in his fright:
peace be to thee; and by way of prophecy, that peace would be wrought for Israel by the Lord, and prosperity given them; or by way of prayer, the Lord grant or send peace:
unto this day it is yet in Ophrah of the Abiezrites; that is, the altar Gideon built remained to the times of Samuel, the writer of this book, and was then to be seen in the city of Ophrah, which belonged to the family of the Abiezrites, who were of the tribe of Manasseh.

it came to pass the same night, that the Lord said unto him--The transaction in which Gideon is here described as engaged was not entered on till the night after the vision.

There - On the top of the rock, as is evident from Judges 6:26, where that which is here expressed only in general, is more particularly described. Jehovah - shalom - That is, the Lord's peace; the sign or witness of God's speaking peace to me, and to his people: or the place where he spake peace to me, when I expected nothing but destruction.