Work of God

What is Jesus saying in John 6:26?
You appreciated the feeding miracle (see Twelve Baskets) but not what it pointed to. You came after Me for the wrong reason.

What is Jesus saying in the first half of John 6:27?
εργαζεσθε (ergazesthe), the original Greek word translated “labor,” is being used not in the sense of holding down a 9 to 5 job but in the sense of endeavoring or striving for something. Jesus is telling them to focus not on filling their bellies but on what “endures unto everlasting life” (John 6:27) - i.e., salvation - that He, the “Son of Man” (John 6:27) will give.

When did “God the Father ... set His seal on” Jesus?
See Lamb of God.

What are they saying in John 6:28?
'So... what are we supposed to do?'

What is Jesus' answer?
Believe in Jesus, whom God the Father has sent: “Believe in Him whom He has sent” (John 6:29).

Believe what about Jesus?
That He is God the Son who so loved us that He paid the death penalty due for our sins, and then rose from the dead to prove His deity, and that we will go to heaven because of what He did for us (see John 3:16 Meaning).

But to go to heaven, don't we still have to do something in addition to believing that?
“For by grace you have been saved through faith, and this is not of yourselves; it is the gift of God, not of works, lest anyone should boast” (Ephesians 2:8-9). “Where then is boasting? It is excluded. By what law? Of works? No, but by the law of faith. Therefore we conclude that a man is justified by faith apart from the works of the law” (Romans 3:27-28). Imagine that you are a death row inmate about to be executed. Just as the lethal injection needle is about to pierce you, the judge who justly sentenced you to death shows up, removes his robe, hands it off to you, tells you that because he loves you he will take your death penalty for you so that you can have life instead of death, then takes the needle, the injection, and dies.

When you are freed and someone asks you, “Hey, you were supposed to be executed; how did you get freed?”, will you say that it was because the just judge who loves you took your death penalty for you but also because you held his robe, or because you did anything else, or will you say that it was 100% because the judge died for you?
 

Does that mean that we shouldn’t do any works?
We should do works, but read 1 Corinthians 3:9-15 carefully: “9 For we are fellow workers of God; you are God’s field, God’s building. 10 According to the grace of God that was given to me, as a wise masterbuilder I have laid the foundation, and another builds on it. But let everyone take heed how he builds on it. 11 For no other foundation can anyone lay than that which is laid, which is Jesus the Christ. 12 Now if anyone builds upon this foundation with gold, silver, precious stones, wood, hay, straw, 13 each one’s work will become evident; for The Day will display it, because it will be revealed by fire; and the fire will test each one’s work, of what sort it is. 14 If anyone’s work which he has built upon it survives, he will receive a reward. 15 If anyone’s work is burned up, he will suffer loss, but he himself will be saved, yet so as through fire.” The “fire” in 1 Corinthians 3:13 is not the fire of hell since this is addressed to “fellow workers of God” (1 Corinthians 3:9) - i.e., Christians. “The Day” in the same verse is the day when Christians die and stand before Jesus, not to be judged between heaven and hell, but to receive in heaven our “reward” based on our “works” on earth, and the “fire” represents the adjudicating eyes of Jesus: “And to the angel of the church in Thyatira write, ‘These things says the Son of God, who has eyes are like a flame of fire, and His feet like burnished bronze: “I know your works, and love, and service, and faith, and your patience, and your works; and the last to be more than the first” (Revelation 2:18-19). If you look carefully at the items listed in 1 Corinthians 3:13, the first three - “gold, silver, precious stones” - are those that will survive the fire, and represent the works done from a true intent to bring glory to God, while the next three items - “wood, hay, straws” - are those that will be burned up in the flames and represent the works done from a heart to glorify oneself or anyone else other than God. If you bring a mountain of work but they were done to bring glory to yourself or anyone else other than God, you will lose your reward in (not "of") heaven, while someone who brings a handful of works that were truly done to glorify God will get their reward. But here is a very important point: 1 Corinthians 3:15 says that even if your mountain of works is burned up and counts for nothing, you yourself still “will be saved.” Why? It's because salvation from sin and into heaven is a free gift from God that doesn't depend on your works. You can't work your way into a free gift. All you can do is to receive it, sincerely thank the Giver, and try your best to live your life to honor and glorify Him.

Do they understand whom Jesus meant by, “Him whom He sent” when He said, “This is the work of God, that you believe in Him whom He sent” in John 6:29?
Yes, the “You” in their response (John 6:30) indicates that they understood it to be Jesus.