One in Messiah Congregation
Let's examine this verse:
Rom.3  Seeing it is one God, which shall justify the circumcision by faith , and uncircumcision through faith .
The letter to the Romans was written in approx 60 AD. Remember at that time the Gentile nations didn't know the Hebrew Scriptures, the God of Israel, the Messiah, or Yeshua the Messiah that rose from the dead. They had to learn from scratch.. Paul had a difficult job. He had to convince people of a God they never heard of; in a language they didn't read; and of a jewish person ( Yeshua ) who rose from the dead and was the Messiah of the Hebrew scriptures.
words to explore:
justify - made righteous, obtain salvation, bring to salvation
circumcision - in this verse, this word is talking about the Jews ( all 12 Tribes )
by faith - by the faith of the God of their forefathers and the Hebrew scriptures pertaining to the Messiah who only has salvation. In other words, the Jewish people in Paul's time already knew the Hebrew scriptures ( Torah, Prophets, and the psalms). They were looking for the Messiah. All they had to do was go back to scripture and recognize the Messiah as many of them did.
uncircumcision - in this verse, this word is talking about the Gentiles
through faith - of the God of Israel, the Hebrew scriptures and the Jewish people who received the Messiah who only has salvation. In other words, the Gentiles in the time of Paul didn't know scripture or anything about the God of Israel. Therefore, they had to be taught Through the Hebrew scriptures ( the word of God ) to find out about God and His Word which is Messiah who was for to come. The Gentiles had to accept the "New Covenant" that was given to Israel ( Jer. 31:33 - all 12 tribes ).
Rom.11  For the gifts and calling of God are without repentance.
John.4[ 22] Ye worship ye know not what: we know what we worship: for salvation is of the Jews. ( where the Messiah comes from )
] What advantage then hath the
Jew? or what profit is there of circumcision?
 Much every way: chiefly, because that unto them were committed the oracles of God. ( they had the word of God from mount Sinai )
Rom.9[1 ] I say the truth in Christ, I lie not, my conscience also bearing me witness in the Holy Ghost,[2 ] That I have great heaviness and continual sorrow in my heart. For I could wish that myself were accursed from Christ for my brethren, my kinsmen according to the flesh: Who are Israelites; to whom pertaineth the adoption, and the glory, and the covenants, and the giving of the law, and the service of God, and the promises Whose are the fathers, and of whom as concerning the flesh Messiah / Christ came, who is over all, God blessed for ever. Amen.
Israelites; to whom pertaineth:
They are God's chosen people. God had chosen the people of Israel, from all of the peoples of the Earth. He made a covenant with them and declared them to be His people, and He to be their God. Out of all the peoples of the earth, Israel received the adoption as sons.
Amos.3[ 2] You only have I known of all the families of the earth....
The Glory of God is in many places in scripture. God met with the people of Israel in the Tabernacle. His glory accompanied them. His Presence went with them.
Exod.33[ 14] And he said, My presence shall go with thee, and I will give thee rest .
Exod.24 [16 ] And the glory of the LORD abode upon mount Sinai, and the cloud covered it six days: and the seventh day he called unto Moses out of the midst of the cloud. [17 ] And the sight of the glory of the LORD was like devouring fire on the top of the mount in the eyes of the children of Israel.
Exod.40[ 34] Then a cloud covered the tent of the congregation, and the glory of the LORD filled the tabernacle. [35 ] And Moses was not able to enter into the tent of the congregation, because the cloud abode thereon, and the glory of the LORD filled the tabernacle.
The covenant God made with Abraham, the covenant God made with Isaac, the covenant God made with Jacob, all of the covenants were given to the people of Israel.
the giving of the law
God met them at the mount and gave to them His commandments.
the service of God
They were instructed on how to worship God in a way that would be pleasing in His sight.
Heb.5[ 4] And no man taketh this honour unto himself, but he that is called of God, as was Aaron . ( priesthood )
All of the promises were given to the Israel of God specifically so that they might claim them and walk in them, and be the recipients of the blessing of the promises.
Whose are the fathers,
Those holy, righteous men like Abraham, Isaac, Jacob, the great patriarchs of Israel were theirs, of the Jews.
and of whom as concerning the flesh Messiah / Christ came,
The ancestry of Messiah. The Messiah who would come in the person of Yeshua / Jesus was revealed to the world the Jewish people.
Jer.31[ 31] Behold, the days come, saith the LORD, that I will make a new covenant with the house of Israel, and with the house of Judah:
 But this shall be the covenant that I will make with the house of Israel;
Do only the Gentiles need Yeshua for Salvation? Do the Jews need the Messiah also?
We all need Messiah Yeshua for Salvation
John.3 [ 36] He that believeth on the Son hath everlasting life: and he that believeth not the Son shall not see life; but the wrath of God abideth on him.
John.5 [ 23] That all men should honour the Son, even as they honour the Father. He that honoureth not the Son honoureth not the Father which hath sent him.
John.14[ 6] Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by me.
Acts.4[ 12] Neither is there salvation in any other: for there is none other name under heaven given among men, whereby we must be saved.
1John.2  Who is a liar but he that denieth that Yeshua / Jesus is the Messiah / Christ? He is antichrist, that denieth the Father and the Son. Whosoever denieth the Son, the same hath not the Father:
1John.5 [[ 10] He that believeth on the Son of God hath the witness in himself: he that believeth not God hath made him a liar; because he believeth not the record that God gave of his Son.[11 ] And this is the record, that God hath given to us eternal life, and this life is in his Son .12] He that hath the Son hath life; and he that hath not the Son of God hath not life.
2John.1 [ 9] Whosoever transgresseth, and abideth not in the doctrine of Messiah / Christ, hath not God.