Hebrews 1:7

Who maketh his angels spirits - They are so far from being superior to Christ, that they are not called God's sons in any peculiar sense, but his servants, as tempests and lightnings are. In many respects they may have been made inferior even to man as he came out of the hands of his Maker, for he was made in the image and likeness of God; but of the angels, even the highest order of them, this is never spoken. It is very likely that the apostle refers here to the opinions of the Jews relative to the angels. In Pirkey R. Elieser, c. 4, it is said: "The angels which were created the second day, when they minister before God, אש של נעשין become fire." In Shemoth Rabba, s. 25, fol. 123, it is said: "God is named the Lord of hosts, because with his angels he doth whatsoever he wills: when he pleases, he makes them sit down; Judges 6:11 ; : And the angel of the Lord came, and sat under a tree. When he pleases, he causes them to stand; Isaiah 6:2 ; : The seraphim stood. Sometimes he makes them like women; Zechariah 5:9 ; : Behold there came two women, and the wind was in their wings. Sometimes he makes them like men; Genesis 18:2 ; : And, lo, three men stood by him. Sometimes he makes them spirits; Psalm 104:4 ; : Who maketh his angels spirits. Sometimes he makes them fire; ibid. His ministers a flame of fire."

In Yalcut Simeoni, par. 2, fol. 11, it is said: "The angel answered Manoah, I know not in whose image I am made, for God changeth us every hour: sometimes he makes us fire, sometimes spirit, sometimes men, and at other times angels." It is very probable that those who are termed angels are not confined to any specific form or shape, but assume various forms and appearances according to the nature of the work on which they are employed and the will of their sovereign employer. This seems to have been the ancient Jewish doctrine on this subject.