The Christian belief is fundamentally based on Paul's teachings, emphasizing that salvation is attained through faith alone in Jesus Christ. This faith is rooted in Christ's sacrificial death and resurrection.
2 Corinthians 1:20 highlights that all of God's promises are fulfilled in Jesus Christ: "For no matter how many promises God has made, they are 'Yes' in Christ. And so through Him the "Amen" is spoken by us to the glory of God" (NIV). If anyone doubts this faith, their salvation will be in vain. Paul further explains in 2 Corinthians 1:21-22;
21 Now it is God who makes both us and you stand firm in Christ. He anointed us, 22 set his seal of ownership on us, and put his Spirit in our hearts as a deposit, guaranteeing what is to come. (NIV)
Simply put, anyone who is not in Christ will not be guaranteed salvation.
Paul's letters to the Corinthians address important Church affairs, including the identification of false teachers who preaching "another Jesus" (2 Corinthians 11:4). Although Paul does not describe the characteristic of this "another Jesus", he warns that "Just as Eve was deceived by the serpent's cunning, your minds may somehow be led astray from your sincere and pure devotion to Christ" (2 Corinthians 11:3).
Therefore it is vital to recognize the words in Matthew 28:18-20, where Jesus says:
18 “All authority in heaven and on earth has been given to me. 19 Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, 20 and teaching them to obey everything I have commanded you. And surely I am with you always, to the very end of the age.” (NIV)
God's promises are always "Yes" in Christ, for Jesus inherents all authority from God.