John 6:26-27 Jesus answered them and said, Verily, verily, I say unto you, You seek me, not because you saw the miracles, but because you did eat of the loaves, and were filled. Labour not for the meat which perisheth, but for that meat which endureth unto everlasting life, which the Son of man shall give unto you: for him hath God the Father sealed. 

The next day, the crowd from the previous day saw that there was no other boat there, except the one His disciples entered with, and that Jesus did not go with His disciples in the boat, but that His disciples left alone. When they, therefore, saw that Jesus was not there, neither His disciples, they also went to Capernaum by ship, seeking Jesus.

When they found Him on the other side of the sea, they asked Him when He came over. Jesus answered them that they seek Him not because they saw miracles, but because He gave them food and they ate; not as being convinced by visible miracles, which should lead godly men to acknowledge Him as Messiah, but as by appetite, which leads sensual men like beasts through the impulse of want and supply.

We get eternal life now and keep it forever if we meet the following conditions: Come to Christ (John 6:37, 44, 45, 65); know God and Christ (John 17:2-3); cause no offense (Matt. 18:8-9); forsake all (Matt. 19:27-29; Mark 10:28-30); overcome sin (Rev. 2:7, 11, 17, 26; 3:5, 12, 21); live free from sin (Rom. 5:21; 6:16-23; 8:1-13; Tit. 2:11-14); fight the good fight of faith; lay hold on it (1Tim. 6:12, 19); be sober and hope to the end for it (Tit. 1:2; 3:7; 1Pet. 1:5, 9, 13); endure temptations (Jas. 1:12); love everybody (1Jn. 3:14-15); keep yourself in the love of God, looking for eternal life (Jude 1:20-24); be faithful unto death (Rev. 2:10; Heb. 12:14-15); believe and obey the gospel (John 3:15-19, 36; 4:14; 5:24; 6:40, 47, 54; 2Cor. 5:17; Rom. 1:5); be born again, hear Christ, and follow Him (John 3:1-36; 10:27-29).

BUT eternal life does not become an unforfeitable eternal possession until we enter into it (Matt. 7:13; 18:8-9; 19:17; Rom. 6:22); receive it (Rom. 6:23; Jas. 1:12; 1Pet. 1:13; Rev. 2:10); reap it (Gal. 6:7-8); and inherit it in the world to come (Matt. 19:27-29; Mark 10:28-30; Luke 18:28-30), and at the end of this life (Rom. 6:22).

‘Him has God the Father sealed’ – confirmed by giving Him the Holy Spirit without measure (John 3:33-34).