30 since there is one God who will justify the circumcised by faith and the uncircumcised through faith.
30 since [it is true] there is one God [God does not operate on multiple ways of salvation] who will [logical progression] justify the circumcised [the Jew] by faith and the uncircumcised [the Gentile] through [the—faith is the only way] faith.
There is only one principle whereby God saves people (by faith) because God remains the same in the way He does things. Since God is one (monotheistic), He must be consistent with Himself. He operates the same way with both Jew and Gentile. Since God is one, He is the God of redemption by faith to all. There is no special group, such as the Jews, that has exclusive salvation.
The future tense of the word “justification” indicates change of status when one places his or her faith in Christ’s work. The future here is not at the final judgment but logical progression indicating permanent purpose of how God works.
Because God is one, He has only one way to save man.
If we do not accept God’s way of saving man, we impugn His character. The law cannot save us; morality cannot, either. We are always saved by faith in God’s provision of the death of Christ for our sins. That is the only way.
Ac 4: 12 Nor is there salvation in any other, for there is no other name under heaven given among men by which we must be saved.
Jn 14: 6 Jesus said to him, “I am the way, the truth, and the life. No one comes to the Father except through Me.”