What does the Bible say about who is a true believer?

According to the Scriptures, a true believer is one who is granted faith by God to believe in Christ. In John 1:47, Jesus refers to Nathanael as 'an Israelite indeed, in whom is no guile,' which highlights that true believers are authentic and sincere, not deceitful. This aligns with Romans 2:28-29, which states that true circumcision is a matter of the heart and spiritual integrity. It is God’s work that transforms individuals into believers, enabling them to trust in Christ with sincerity and truth.