Faith is work, our Lord said so. The people asked what shall we do! Jesus had a great opportunity to correct them, but He did not say to them " You cannot do any work", He told them to believe in Him, this is the work of God! Christ responded: “This is the work of God (i.e., from God – a genitive of source), that you believe on him whom he has sent” (6:29). It is not God who believes for you, yet He is the source in which we can believe, but it is the people who must put their trust in Christ. When the Philippian Jailor asked "WHAT MUST WE DO?" Maybe Paul should have told him: "There is nothing you can do" and then maybe Jesus should have said the same thing.