john 13:18 I speak not of you all: I know whom I have chosen: but that the scripture may be fulfilled, He that eateth bread with me hath lifted up his heel against me. - Free Bible Online

      18, 19. I speak not of you all--the "happy are ye," of Joh 13:17, being on no supposition applicable to Judas.
      I know whom I have chosen--in the higher sense.
      But that the scripture may be fulfilled--that is, one has been added to your number, by no accident or mistake, who is none of Mine, but just that he might fulfil his predicted destiny.
      He that eateth bread with me--"did eat of my bread" (Ps 41:9), as one of My family; admitted to the nearest familiarity of discipleship and of social life.
      hath lifted up his heel against me--turned upon Me, adding insult to injury. (Compare Heb 10:29). In the Psalm the immediate reference is to Ahithophel's treachery against David (2Sa 17:1-23), one of those scenes in which the parallel of his story with that of His great Antitype is exceedingly striking. "The eating bread derives a fearful meaning from the participation in the sacramental supper, a meaning which must be applied for ever to all unworthy communicants, as well as to all betrayers of Christ who eat the bread of His Church" (STIER, with whom, and others, we agree in thinking that Judas partook of the Lord's Supper).

JFB.