What does the Bible say about eternal security for believers?

According to John 10:27-30, Jesus affirms that His sheep, those who genuinely believe in Him, are granted eternal life and shall never perish. This promise signifies that no one can remove them from the Father's hand. The assurance of eternal security is central to the believer's faith, as salvation is not dependent on human effort but on God's sovereign grace. In 1 John 2:19, it is also made clear that those who abandon their faith were never truly part of the flock, illustrating the permanence of true salvation.