You see, before one could redeem his brother, according to law, their had to be a union of relationship prior existing ! It is called a kinsmen redeemer ! It is Illustrated in Ruth 3:9-13
9 And he said, Who art thou? And she answered, I am Ruth thine handmaid: spread therefore thy skirt over thine handmaid; for thou art a near kinsman.
10 And he said, Blessed be thou of the Lord, my daughter: for thou hast shewed more kindness in the latter end than at the beginning, inasmuch as thou followedst not young men, whether poor or rich.
11 And now, my daughter, fear not; I will do to thee all that thou requirest: for all the city of my people doth know that thou art a virtuous woman.
12 And now it is true that I am thy near kinsman: howbeit there is a kinsman nearer than I.
13 Tarry this night, and it shall be in the morning, that if he will perform unto thee the part of a kinsman, well; let him do the kinsman's part: but if he will not do the part of a kinsman to thee, then will I do the part of a kinsman to thee, as the Lord liveth: lie down until the morning.
Ruth 4:
Then went Boaz up to the gate, and sat him down there: and, behold, the kinsman of whom Boaz spake came by; unto whom he said, Ho, such a one! turn aside, sit down here. And he turned aside, and sat down.
2 And he took ten men of the elders of the city, and said, Sit ye down here. And they sat down.
3 And he said unto the kinsman, Naomi, that is come again out of the country of Moab, selleth a parcel of land, which was our brother Elimelech's:
4 And I thought to advertise thee, saying, Buy it before the inhabitants, and before the elders of my people. If thou wilt redeem it, redeem it: but if thou wilt not redeem it, then tell me, that I may know: for there is none to redeem it beside thee; and I am after thee. And he said, I will redeem it.
5 Then said Boaz, What day thou buyest the field of the hand of Naomi, thou must buy it also of Ruth the Moabitess, the wife of the dead, to raise up the name of the dead upon his inheritance.
6 And the kinsman said, I cannot redeem it for myself, lest I mar mine own inheritance: redeem thou my right to thyself; for I cannot redeem it.
7 Now this was the manner in former time in Israel concerning redeeming and concerning changing, for to confirm all things; a man plucked off his shoe, and gave it to his neighbour: and this was a testimony in Israel.
Christ had a kinsman right to redeem the Elect chosen in Him before the world Began Eph 1:4 !
Without that established legal Union, Christ could not have come into the world to redeem them Gal 4:4-5
4 But when the fulness of the time was come, God sent forth his Son, made of a woman, made under the law,
5 To redeem them [His Kinsmen] that were under the law, that we might receive the adoption of sons.
But now, Jesus Christ never had a kinsman relationship with the serpents seed Gen 3:14-15
14 And the Lord God said unto the serpent, Because thou hast done this, thou art cursed above all cattle, and above every beast of the field; upon thy belly shalt thou go, and dust shalt thou eat all the days of thy life:
15 And I will put enmity between thee and the woman, and between thy seed and her seed; it shall bruise thy head, and thou shalt bruise his heel.
There is no redemption by Christ for the serpents seed, or the children of the devil ! For they were never in Christ Eph 1:4