Joh 3:18 …condemned already, because he has not believed in the name of the only begotten Son of God. (b)
In Rom 9, Paul discusses how the Gentiles were made righteous while Israel was left behind. The Gentiles pursued (responded) to righteousness by faith, “the people of Israel, who tried so hard to get right with God by keeping the law, never succeeded. Why not? Because they were trying to get right with God by keeping the law instead of by trusting in him. They stumbled over the great rock in their path” (Rom 9:30-32 (NLT). Their unbelief became a stumbling block.
Gentiles received “imputed righteousness“. To “impute” is to represent, ascribe or attribute something to someone other than yourself. 2Cor 5:21 “For He made Him who knew no sin to be sin for us, that we might become the righteousness of God in Him”, meaning God treated Jesus as though He lived our lives of sin and treated us as though we lived His life of righteous perfection. The moment we place our faith in Christ, God ascribes the perfect righteousness of Christ to our account and thereby “…be found in Him, not having my own righteousness, which is from the law, but that which is through faith in Christ, the righteousness which is from God by faith;” (Phi 3:7-9). This how we become perfect (positionally) in His sight.