What does John 6:39 mean?
The crowds who followed Jesus were attracted to His miracles, but misunderstood them. They are still fixated on free food, entertainment, and the idea that their salvation depends on good works. Jesus has been explaining the truth behind all of these "signs" that He, the Bread of Life, has been sent into the world so that all who believe in Him can have eternal life.In the prior verses, Jesus has explained that His words and deeds are ordained by God the Father. In particular, Jesus has referred to the idea that God the Father "gives" people to Christ for salvation, and that all such people will be accepted by Jesus (John 6:37). Here, Jesus uses that same concept to claim that those whom God has given to Him will—undoubtedly—see eternal life. This is a crucial statement on the question of eternal security: according to Jesus, those who have come to Him in belief, as given by God the Father, are absolutely guaranteed not to be "lost," and are assured of being [raised] up on the last day."
Put another way, those who come to Christ will be accepted (John 3:16–17), and will see eternal life. They will not be rejected by Christ (Matthew 7:7–8), and they will not fail to maintain that salvation until the end.