According to Paul sinners have no excuse. They reveal that they know what is right and what is wrong as they condemn others, and thus they are worthy of God’s condemnation:
Therefore you are without excuse, every man of you who passes judgment, for in that you judge another, you condemn yourself; for you who judge practice the same things. And we know that the judgment of God rightly falls upon those who practice such things. And do you suppose this, O man, when you pass judgment upon those who practice such things and do the same yourself, that you will escape the judgment of God? Or do you think lightly of the riches of His kindness and forbearance and patience, not knowing that the kindness of God leads you to repentance? (Rom. 2:1-4).
Paul said the reason for God’s forbearance and patience is to give people opportunity to repent. Furthermore, as Paul continued, he revealed that only those who repent and live holy lives will inherit God’s kingdom:
But because of your stubbornness and unrepentant heart you are storing up wrath for yourself in the day of wrath and revelation of the righteous judgment of God, who will render to every man according to his deeds: to those who by perseverance in doing good seek for glory and honor and immortality, eternal life; but to those who are selfishly ambitious and do not obey the truth, but obey unrighteousness, wrath and indignation. There will be tribulation and distress for every soul of man who does evil, of the Jew first and also of the Greek, but glory and honor and peace to every man who does good, to the Jew first and also to the Greek (Rom. 2:5-10).
Clearly, Paul would not agree with those who teach that people who just “accept Jesus as Savior” are guaranteed eternal life. Rather, it is those who repent and “who by perseverance in doing good seek for glory and honor and immortality.”
But does this not indicate that people can continue to practice religions other than Christianity and be saved as long as they repent and obey God?
No, there is no salvation apart from Jesus for a number of reasons, one of which is that only Jesus can set people free from their enslavement to sin.
But if they want to repent, how will they know to call on Jesus if they have never heard of Him?
God, who knows the hearts of all people, will reveal Himself to anyone who is sincerely seeking. Jesus promised, “Seek and you will find” (Matt. 7:7), and God expects everyone to seek Him (see Acts 17:26-27). When He sees a person whose heart is responding to His relentless evangelization, He will send the gospel to that person, just as He did for the Ethiopian eunuch and Cornelius’ household. God is not even limited by the church’s participation, as He proved in the conversion of Saul of Tarsus. If there is no one to take the gospel to a sincere seeker, God will go Himself! I’ve heard numerous contemporary instances where people in closed countries have been converted by visions they had of Jesus.
