“For the Scripture says, “Everyone who believes in him will not be put to shame.” For there is no distinction between Jew and Greek; for the same Lord is Lord of all, bestowing his riches on all who call on him. For “everyone who calls on the name of the Lord will be saved.” (Romans 10:11-13)
Saint Paul preached primarily to the Gentiles but he hoped the Jews too would hear and believe the gospel. He knew that though many of them were zealous for the things of the Lord, their desires and sincerity were insufficient for salvation. Perhaps their zeal was based solely on their own self-righteousness, their need to glorify and exalt themselves. Perhaps they were proud of their Law-keeping, their morality, proud that they were better than everyone else simply because they were Jews. If so, then even though they claimed to follow the Lord and do His will, they really stood in rebellion against Him. In order to become right with God they had to renounce their own righteousness, repent and believe in the righteousness of Jesus on their behalf.
This truth applies to all people of all religions, including Judaism, nominal or apostate Christianity, and any belief system based on righteousness by works or heritage. No one is granted membership in the Kingdom of God unless they repent of their sins and self-centeredness and by faith trust in Jesus. All who practice salvation by works, all who do not come through Jesus, are lost no matter how moral they seem or claim to be.
In God’s mysterious and awesome way He calls upon His People to fulfill a calling through preaching and evangelism to both Jew and pagan. For in order to be saved, sinners must call on the name of the Lord and for that to happen they must know of the death and resurrection of Jesus. For that to happen, someone must tell them. God in His sovereign will has chosen believers to be that someone, to be His instruments to proclaim the gospel. Thus we are to preach to all that they can have the opportunity to hear the truth and thus be saved by faith in Jesus alone.