Romans 3: 30, “since indeed God who will justify the circumcised by faith and the uncircumcised through faith is one.” (NASB)
To understand this passage we need to that the Jews were willing to allow the Gentiles to be on the same level with them. See that felt that because they came up under the Law, with all its rites, ceremonies, and rituals, that the Gentile, who were just pagans and unclean heathens, could not obtain a just standing with the LORD God. But the Holy Spirit through Paul is making it very clear that there is One God, one Salvation, and it is through and by the Belief on the Christ and Him Crucified.
Remember that justification is a legal position in acted by a judge. Our judge in the Just and Righteous LORD God and this right stand is afforded to us by the Blood of the Son of God. The Spirit of the Lord wants to make it plain and straight that there is only One who can and has justifies.