9 And now addressing the few that remained: “Then said Jesus to the twelve” (namely, those twelve who remained), “Will ye also,” said He, “go away?” Not even Judas departed. But it was already manifest to the Lord why he remained: to us he was made manifest afterwards. Peter answered in behalf of all, one for many, unity for the collective whole: “Then Simon Peter answered Him, Lord, to whom shall we go?” You drive us from You; give us Your other self. “To whom shall we go?”
If we abandon You, to whom shall we go? “You have the words of eternal life.” See how Peter, by the gift of God and the renewal of the Holy Spirit, understood Him. How other than because he believed? “You have the words of eternal life.” For You have eternal life in the ministration of Your body and blood. “And we have believed and have known.” Not have known and believed, but “believed and known.” For we believed in order to know; for if we wanted to know first, and then to believe, we should not be able either to know or to believe. What have we believed and known? “That You are Christ, the Son of God;” that is, that You are that very eternal life, and that You give in Your flesh and blood only that which You are.
Source: Tractates on the Gospel of John (New Advent)