Jesus replies that the work required of them is faith in Him whom God has sent. The questioners conceive of work in terms of earning merit, but Jesus at once draws attention to the need for faith. Pray and work. While he had spent much time ministering to men's bodily needs, the real purpose of his coming into the world was to save men's souls. Faith in Christ is the great saving work.
Faith is work.
Faith and work are one. Faith is the work in which all works is embodied. Be there a true perfect faith, and all works of righteousness will come into it and be one with it. We have mourned over men as fallen creatures because they have risen against the systmes in which they were reared. But possibly we are wrong.