No angel is a son of God. Therefore, this verse continues speaking of Christ's glory and greatness. And again, when he bringeth in the firstbegotten into the world, he saith, And let all the angels of God worship him. Christ is far greater than the angels. And of the angels he saith, Who maketh his angels spirits, and his ministers a flame of fire.
Angels are spirits whereas believers are flesh and blood.
And they're made so by Christ. So Christ is the Creator of the angels. Fire has to do with the altar and judgment. Compare verse 7 with verse 14. No angel is a son.