1. Christ who received Jews and Gentiles (Rom 15:8-12)
    Ps 18:49, Deut 32:43, Ps 117:1, Isa 11:10

By being circumcised, Jesus revealed the truthfulness of God in the promises of Christ prophesied in the Old Testament. (Rom 15:8)

Rom 15:8 Now I say that Jesus Christ was a minister of the circumcision for the truth of God, to confirm the promises made unto the fathers:

Also, by completing the Old Testament law, Jesus made it possible for Gentiles who believe in Jesus to be the Christ to dwell in God’s mercy. (Rom 15:9-12)

Rom 15:9 And that the Gentiles might glorify God for his mercy; as it is written, For this cause I will confess to thee among the Gentiles, and sing unto thy name.
10 And again he saith, Rejoice, ye Gentiles, with his people.
11 And again, Praise the Lord, all ye Gentiles; and laud him, all ye people.
12 And again, Esaias saith, There shall be a root of Jesse, and he that shall rise to reign over the Gentiles; in him shall the Gentiles trust.

So Gentiles who believe in Jesus as the Christ can rejoice in God with the Jews in Christ. (Ps 18:49, Deut 32:43, Ph 117:1, Isa 11:10)

Ps 18:49 Therefore will I give thanks unto thee, O Lord, among the heathen, and sing praises unto thy name.

Deut 32:43 Rejoice, O ye nations, with his people: for he will avenge the blood of his servants, and will render vengeance to his adversaries, and will be merciful unto his land, and to his people.

Ps 117:1 O praise the Lord, all ye nations: praise him, all ye people.

Isa 11:10 And in that day there shall be a root of Jesse, which shall stand for an ensign of the people; to it shall the Gentiles seek: and his rest shall be glorious.