“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)
Many billions of people think they can earn their way into God’s favor, whatever form they think He may take. They think they can make it to heaven or Nirvana or whatever simply by doing good deeds, or by doing enough good and charitable works to out weight the bad they do, if any.
In the time of Saint Paul, many of the Jews were such a people, zealous for the things of the Lord. Nonetheless, their desires and zeal were insufficient to reconcile them to God, to guarantee eternal salvation. This is probably because their zeal was often based on their own self-righteousness which made them proud of their Law-keeping, their morality, proud that they were better than everyone else simply because they were Jews. 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 Jesus. He was righteous on behalf of the Jews and of all human beings.
This truth applies to all people. People who espouse any religion, including Judaism, nominal or apostate Christianity, and any belief system based on righteousness by works or heritage cannot get to heaven based on their religious deeds. 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 the gospel to all. 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 love, life, 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.