John Calvin on John 13:17

17. If you know these things. He declares that they are happy, if they know and do these things; for knowledge is not entitled to be called true, unless it produce such an effect on believers as to lead them to conform themselves to their Head. On the contrary, it is a vain imagination, when we look upon Christ, and the things which belong to Christ, as separate from ourselves. We may infer from this that, until a man has learned to yield to his brethren, he does not know if Christ be the Master. Since there is no man who performs his duty to his brethren hi all respects, and since there are many who are careless and sluggish in brotherly offices, this shows us that we are still at a great distance from the full light of faith.

John 13:18-20

18. I speak not of you all; I know whom I have chosen; but that the Scripture may be fulfilled, He who eateth bread with me hath lifted up his heel against me. 19. I tell you this now, before it happen, that when it shall have happened, you may believe that I am. “Que ce suis-je;” — “that I am he.” 20. Verily, verily, I tell you, if I send any one. he who receiveth him receiveth me; and he who receiveth me receiveth him who sent me.