The disciples finally understand that Jesus knows everything. While they do not yet understand everything as Jesus reveals it to them, they believe. Knowing all they do, and seeing all they have, they cling to every word Jesus is speaking as the prophecy unravels before their eyes, of the Messiah. The disciples are grieving that Jesus is telling them He is leaving, but assures them that it is best He does, because if He doesn't, the Advocate won't come.