The work is to believe in the one He sent.
To "Work" is aspirational: unto something. To "know" per John 17:3, is also aspirational, also unto something: "That they all may be one; as thou, Father, art in me, and I in thee, that they also may be one in us: that the world may believe that thou hast sent me."John 17:21 (KJV)
Which do you suppose can only come before the other?