Gen 3:15 I will put enmities between thee and the woman, and thy seed and her seed: she shall crush thy head, and thou shalt lie in wait for her heel.
Rev 12:17 And the dragon was angry against the woman: and went to make war with the rest of her seed, who keep the commandments of God, and have the testimony of Jesus Christ.
Haydock commentary: Christ crushed the serpent’s head by his death, suffering himself to be wounded in the heel. His blessed mother crushed him likewise, by her co-operation in the mystery of the Incarnation; and by rejecting, with horror, the very first suggestions of the enemy, to commit even the smallest sin. (St. Bernard, ser. 2, on Missus est.) “We crush,” says St. Gregory, Mor. 1. 38, “the serpent’s head, when we extirpate from our heart the beginnings of temptation, and then he lays snares for our heel, because he opposes the end of a good action with greater craft and power.” The serpent may hiss and threaten; he cannot hurt, if we resist him.
Mary, the second Eve, undid the evil of the first Eve and the crushing did not take place until the second Eve, Mary. As the Old Testament is a foreshadowing of the New, the righteous line of Abel, and Seth after Abel’s Death, contrasted with the unrighteous line of Cain which foreshadows the righteous seed of our spiritual Mother Mary mentioned in Rev 12:17 in the words “Her seed”.
The unrighteous line of those whose father is the Devil is seen in John 8:44 with Jesus speaking to the Pharisees “You are of your father the devil, and the desires of your father you will do. He was a murderer from the beginning, and he stood not in the truth; because truth is not in him. When he speaketh a lie, he speaketh of his own: for he is a liar, and the father thereof.”
Mary is our spiritual Mother and it is Her seed, the faithful, that are adoptive brothers of Jesus. Those who are of the Devil are of the ones spoken of as “thy seed” in Gen 3:15.