Albert Barnes' Notes on the Whole Bible - 1 Chronicles 21:18
It has been observed that it is only in books of a late period that Angels are brought forward as intermediaries between God and the prophets. This, no doubt, is true; and it is certainly unlikely that the records, from which the author of Chronicles drew, spoke of Gad as receiving his knowledge of God’s will from an angel. The touch may be regarded as coming from the writer of Chronicles himself, who expresses the fact related by his authorities in the language of his own day (see Zechariah... read more
The Pulpit Commentary - 1 Chronicles 21:26
He answered him from heaven by fire . There is no doubt significance in the fact that the compiler of Chronicles records this answer by fire, unmentioned in the Book of Samuel. He would give prominence to this great token, as determining, or going a great way towards determining, the site of the temple. The answer by fire was given on critical and special occasions (Le 1 Chronicles 9:24 ; 1 Kings 18:24 , 1 Kings 18:38 ). read more