Jesus answered them, “This is the work of God, that you believe in him whom he has sent.”
29. The work of God is this. They had spoken of works Christ reminds them of one work, that is, faith; by which he means that all that men undertake without faith is vain and useless, but that faith alone is sufficient, because this alone does God require from us, that we believe For there is here an implied contrast between faith and the works...
Whether this conference was with the Capernaites, in whose synagogue Christ now was, or with those who came from the other side of the sea, is not certain nor material; however, it is an instance of Christ's condescension that he gave them leave to ask him questions, and did not resent the interruption as an affront, no, not from his common hearers, though not his immediate followers.
Commenting on John 6:28-59
They said therefore unto him,.... Seeing he proposed believing in him as the grand work of God to be done, and what is most acceptable in his sight: what sign showest thou then, that we may see and believe thee?