How can we be sure that God cannot lose one sheep?

In John 6:37-39, Jesus states, 'All that the Father giveth me shall come to me; and him that cometh to me I will in no wise cast out.' This promise reinforces the security of believers in Christ, affirming that every individual chosen by the Father will be preserved. The emphasis on God’s sovereign will ensures that nothing can thwart His purpose in salvation. These verses provide great comfort to believers, as it guarantees eternal security in Christ—confirming that those the Father has called will never be lost or cast away.