Isaías 10
Ambrose of Milan · Comentário Patrístico (catena)
Isaías 10:17
And Isaiah shows that the Holy Spirit is not only light but also fire, saying, "And the light of Israel shall be for a fire." So the prophets called him a burning fire, because in those three points we see more intensely the majesty of the Godhead; since to sanctify is of the Godhead, to illuminate is the property of fire and light, and the Godhead is customarily pointed out or seen in the appearance of fire: "For our God is a consuming fire," as Moses said. — On the Holy Spirit 1.14
Isaías 10:21-22
This is therefore what the patriarch Isaac said: You will serve your brother. But when you have removed and freed yourself from his yoke on your neck, he is signifying two future peoples, one the son of a handmaid, the other of a free woman (for the letter is a servant, but grace is free), and that people who adheres to the letter will be a servant as long as they follow the interpreter of spiritual doctrine. Then also what the Apostle said will come to pass: That the remnants may be saved according to the choice of grace. Serve your brother, therefore: but then you will feel the benefit of servitude when you begin to obey your brother willingly, rather than forcibly. — On Jacob and the Blessed Life, 3.13