What does the Bible say about the security of believers in Christ?

In John 10:27-29, Jesus emphasizes the absolute security of His followers, affirming that His sheep hear His voice and that He knows them intimately. He promises that they shall never perish and assures them that no one can pluck them out of His hand. This signifies the eternal life given to believers, which is secured by Christ's atoning sacrifice. Thus, the believer's security is not based on their own actions but is fully grounded in Christ's work upon the cross, highlighting the magnificence of God's grace towards His elect.