Believe
The church controversy in that time was how Jews and non-Jews could worship together. Paul emphasizes that belief in Jesus is all that is needed. Therefore, all have equal access to all the benefits of being a Christian. He goes on to say we must tell other people about Jesus so they can believe too.
Belief in Jesus should be the theme of our lives. We should believe in Jesus to receive forgiveness and eternal life, have ever-growing belief in Jesus to live a life more obedient to Him, and have the courage to tell others about Jesus so they can believe in Him.