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 in 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.

If ye know these things, happy, etc. - True happiness consists in the knowledge of God, and in obedience to him. A man is not happy because he knows much; but because he receives much of the Divine nature, and is, in all his conduct, conformed to the Divine will. "They who have read many books (says Menu) are more exalted than such as have seldom studied; they who retain what they have read, than forgetful readers; they who fully understand, than such as only remember; and they who perform their known duty, than such as barely know it. Sacred knowledge and devotedness to God are the means by which a man can arrive at beatitude." See Institutes of Menu, c. xii. Inst. 103, 104. For a heathen this saying is very remarkable.

If ye know these things,.... The duties they owed to him, and one another; those kind offices of love and respect to each other; the humility, condescension, and brotherly love, which ought to be in them, and of which he had given them an example:
happy are ye if ye do them; for the bare theory, or a mere speculative knowledge of these things, is not sufficient; not he that knows and does not, but he that knows and does his master's will, is blessed; he is blessed with communion with his Lord, and shall hereafter enter into his joy, with "well done good and faithful servant". There is an happiness "in" doing well, and which follows "on" it, though not "for" it, in a way of merit; on the other hand, persons who know and do not, are very unhappy; the Jews have a saying (a),
, "he that learns but not to do", it would have been better for him, if he had never been created; and says R. Jochanan, he that learns but not to do, it would have been better for him if his secundine had been turned upon his face, and he had never come into the world.''
(a) Hieros. Beracot, fol. 3. 2.

If ye know these things, happy are ye if ye do them. Know what things? Of course they knew that Christ had washed their feet. But did they know what he meant? The meaning is clearly, "If ye understand the meaning of my act, happy are ye if ye exemplify the same spirit in your lives."