In being made of a woman and made under law, He took on the seed of Abraham and not the seed of mankind in general, for all mankind is not the Seed of Abraham Heb 2:16
16 For verily he took not on him the nature of angels; but he took on him the seed of Abraham.
Now in taking on the seed of Abraham, Paul says that He was made sin for us !
2 Cor 5:21
21 For he hath made him to be sin for us [The seed of Abraham], who knew no sin; that we might be made the righteousness of God in him.
Who are the us in 2 Cor 5:21 that Paul is referring to ? Is it all mankind without exception ? No it is not. Let us examine the scripture to find the answer. " When the fulness of time had come, God sent forth His own Son [meaning He was God's Son before Mary's Son], made of a women, made under the law, to redeem [ not to make redemption possible] them [ His members, His body] that were under the Law [Limited redemption]that [in order that] they may receive the adoption of Sons.
Now coming as such [ under the law] He came and took upon Him the seed of Abraham. The seed of Abraham is a chosen people !
Ps 105:6
O ye seed of Abraham his servant, ye children of Jacob his chosen.
Isa 41:8
But thou, Israel, art my servant, Jacob whom I have chosen, the seed of Abraham my friend.
So its plain that He came and Identified with and to redeem a Chosen People, and not the whole world of mankind.
In taking on the seed of Abraham, He took on all their Transgressions, and died for their sins !
Isa 53:4-11
4 Surely he hath borne our [seed of Abraham] griefs, and carried our sorrows: yet we did esteem him stricken, smitten of God, and afflicted.
5 But he was wounded for our transgressions, he was bruised for our iniquities: the chastisement of our peace was upon him; and with his stripes we are healed.
6 All we like sheep have gone astray; we have turned every one to his own way; and the LORD hath laid on him the iniquity of us all.
7 He was oppressed, and he was afflicted, yet he opened not his mouth: he is brought as a lamb to the slaughter, and as a sheep before her shearers is dumb, so he openeth not his mouth.
8 He was taken from prison and from judgment: and who shall declare his generation? for he was cut off out of the land of the living: for the transgression of my people was he stricken.
9 And he made his grave with the wicked, and with the rich in his death; because he had done no violence, neither was any deceit in his mouth.
10 Yet it pleased the LORD to bruise him; he hath put him to grief: when thou shalt make his soul an offering for sin, he shall see his seed [The seed of Abraham], he shall prolong his days, and the pleasure of the LORD shall prosper in his hand.
11 He shall see of the travail of his soul, and shall be satisfied: by his knowledge shall my righteous servant justify many [The seed of Abraham]; for he shall bear their [The seed of Abraham] iniquities.
1 Cor 15:3
3 For I delivered unto you first of all that which I also received, how that Christ died for our [The seed of Abraham] sins according to the scriptures;
Yes, in all places above where we see the pronouns our, us, we, their, it refers to the Seed of Abraham !
Lets not forget it is written that He took on the seed of Abraham Heb 2:16
16 For verily he took not on him the nature of angels; but he took on him the seed of Abraham.