Do not work for food that spoils. Work for food that lasts forever. That is the food the Son of Man will give you. God the Father has put his seal of approval on him.” Then they asked him, “What does God want from us? What works does he want us to do?” Jesus answered, “God’s work is to believe in the One he has sent.” John 6.27-29.
At the start of Jesus’ ministry, when he encountered the woman at the well in Samaria, he had drawn for her a contrast between the kind of water that you pour in a cup — H²O — and “living water” … water that “flows up into eternal life” (John 4.10-14). Now he draws a similar contrast between the kind of bread that you consume by eating and the kind of “food that last for ever”, ie food that, like the living water, produces eternal life in the one who partakes of it. And in both cases, Jesus presents himself as the one who can supply the spiritual sustenance that is on offer. “Anyone who drinks the water I give him will never be thirsty” (John 4.14). “No one who comes to me will ever go hungry” (John 6.35).
But Jesus has said that you have to work for this bread of life just as you have to work for bread of the perishing kind. So what is the work that God requires of those who want to acquire the “food that lasts for ever”? Jesus tells them: “It is simply to believe in the One he has sent.” The reference there is to one of the closing promises of the Old Testament from four centuries earlier: “The LORD who rules over all says, ‘I will send my messenger. He will prepare my way for me. Then suddenly the Lord you are looking for will come to his temple. The messenger of the covenant will come. He is the one you long for'” (Malachi 3.1).
It is tempting to paraphrase what Jesus says as “The work God requires of you is that you have faith in me, the messenger of the covenant.” But John never uses the noun pistis; instead he always uses the verb pisteuein — “to believe” — because, for John, what Jesus is talking about is active engagement with Jesus rather than mere intellectual assent to who he is and what he says. And he uses the present continuous tense of the verb “to believe” … “that you believe and go on believing”. The work of God that brings the living water and the food that lasts for ever is my ongoing trustful active relationship with Jesus. It is a life of faith rather than an act of faith … and it is something I have to “work at”, just as I have to work at any relationship that I want to keep fresh and alive and healthy and true.