While I'm at it, I might as well give you Dr. Carson's as well, v27-29 this time:
6:27. When Jesus tells the people not to work for food that spoils, he is rebuking their purely materialistic notions of the kingdom (cf. v. 15). Like the woman at the well who was eager to be supplied with an endless supply of natural water, a supply that would eliminate the need to make frequent trips to the well (4:15), so these people hanker after a miracle-worker who will fill their stomachs with bread (6:26). Though the bread they had eaten the day before was miraculously produced, it was after all merely physical, ‘destined to perish with use’ (Col. 2:22). Men and women should pour their energy into pursuing (i.e. they should ‘work for’) food that endures to eternal life (cf. ‘a spring of water welling up into eternal life’, 4:14). The continuing discourse shows that the ‘food’ is Jesus himself, but the idea is not so much that Jesus endures forever as that, because this food endures, the life it sustains goes on into eternity. On eternal life, cf. notes on 3:15.
It is not entirely clear whether the antecedent of which is the ‘food’ or the ‘eternal life’. If the former, it will shortly become clear that Jesus not only gives the food, he is himself the bread of life (vv. 35, 53). Either way, it is the Son of Man who will give it. If the tense is genuinely future-referring, it is looking to the time after Jesus’ glorification when the Son’s gifts, mediated by the Spirit, are richly bestowed (7:39; 14:15ff.; 16:7). If they ought to ‘work for’ the food that endures unto eternal life, they must also recognize that it is the Son alone who can give it. Jesus prefers not to use a term such as ‘Messiah’ in the context of such heated messianic/political expectations; he opts for Son of Man, a more ambiguous term which nevertheless is increasingly laden, in John, with associations of revelation brought from heaven to earth (cf. notes on 1:51; 3:13; 5:27). This Son of Man, Jesus insists, is the one on whom the Father has placed his seal of approval. The idea is that God has certified the Son as his own agent, authorizing him as the one who alone can bestow this food. God has attested the Son, in much the same way that someone who accepts the Son’s testimony thereby attests or certifies (the same verb) that God himself is truthful. When God ‘placed his seal of approval’ on the Son is not specified. If we are to think of a specific time (though the aorist tense of the verb does not require that we so limit ourselves), perhaps the reference is to Jesus’ baptism (cf. 1:31–34).
6:28. The crowd misunderstands the thrust of Jesus’ prohibition. His words ‘Do not work for food that spoils’ (v. 27) did not focus on the nature of work, but on what is or is not an appropriate goal. His point was not that they should attempt some novel form of work, but that merely material notions of blessing are not worth pursuing. They respond by focusing all attention on work: (lit.) ‘What must we do in order to work the works of God?’ The expression ‘the works of God’ does not refer to the works that God performs, but (as in NIV) to the works God requires. Their question therefore resolves into this: Tell us what works God requires, and we will perform them. From John’s perspective, their naïveté is formidable. They display no doubt about their intrinsic ability to meet any challenge God may set them; they evince no sensitivity to the fact that eternal life is first and foremost a gift within the purview of the Son of Man (v. 27).
6:29. Jesus sets them straight: The work of God—i.e. what God requires—is faith. This is not faith in the abstract, an existential trust without a coherent object. Rather, they must believe in the one [God] has sent. Such language may reflect a specific Old Testament passage, such as Malachi 3:1 where God promises to send, in due time, the ‘messenger of the covenant’, but in fact the language is reminiscent of the entire ‘sentness’ theme in the Fourth Gospel. Jesus is supremely the one who reveals God to us, precisely because, unlike any other person, he has been in the courts of heaven and has been sent from there so that the world might be saved through him (e.g. 3:11–17). Faith, faith with proper Christological object, is what God requires, not ‘works’ in any modern sense of the term. And even the faith that we must exercise is the fruit of God’s activity (cf. notes on vv. 44, 65). Although the noun ‘faith’ is not used, this ‘work of God’ turns out to be nothing else than faith, making this ‘work of God’ diametrically opposed to what Paul means by ‘the works of the law’. As a result, the thought of the passage is almost indistinguishable from Paul: ‘For we maintain that a man is justified by faith apart from observing the law’ (Rom. 3:28). ~Carson, D. A. (1991). The Gospel according to John (pp. 284–285). Leicester, England; Grand Rapids, MI: Inter-Varsity Press; W.B. Eerdmans.
--David