12 But it becomes us rather to inquire what is to be understood by this serving of Christ to which there is attached so great a reward. For if we have taken up the idea that the serving of Christ is the preparation of what is needful for the body, or the cooking and serving up of food, or the mixing of drink and handing the cup to one at the supper table; this, indeed, was done to Him by those who had the privilege of His bodily presence, as in the case of Martha and Mary, when Lazarus also was one of those who sat at the table.
But in that sort of way Christ was served also by the reprobate Judas; for it was he also who had the money bag; and although he had the exceeding wickedness to steal of its contents, yet it was he also who provided what was needful for the meal. And so also, when our Lord said to him, “What you do, do quickly,” there were some who thought that He only gave him orders to make some needful preparations for the feast-day, or to give something to the poor. In no sense, therefore, was it of this class of servants that the Lord said, “Where I am, there shall also my servant be,” and “If any man serve me, him will my Father honor;” for we see that Judas, who served in this way, became an object of reprobation rather than of honor.
Why, then, go elsewhere to find out what this serving of Christ implies, and not rather see its disclosure in the words themselves? For when He said, “If any man serve me, let him follow me,” He wished it to be understood just as if He had said, If any man does not follow me, he serves me not. And those, therefore, are the servants of Jesus Christ, who seek not their own things, but the things that are Jesus Christ's. For “let him follow me” is just this: Let him walk in my ways, and not in his own; as it is written elsewhere, “He that says he abides in Christ, ought himself also so to walk, even as He walked.” For he ought, if supplying food to the hungry, to do it in the way of mercy and not of boasting, seeking therein nothing else but the doing of good, and not letting his left hand know what his right hand does; in other words, that all thought of self-seeking should be utterly estranged from a work of charity.
He that serves in this way serves Christ, and will have it rightly said to him, “Inasmuch as you did it unto one of the least of those who are mine, you did it unto me.” And thus doing not only those acts of mercy that pertain to the body, but every good work, for the sake of Christ (for then will all be good, because “Christ is the end of the law for righteousness to every one that believes”), he is Christ's servant even to that work of special love, which is to lay down his life for the brethren, for that were to lay it down also for Christ.
For this also will He say hereafter in behalf of His members: Inasmuch as you did it for these, you have done it for me. And certainly it was in reference to such a work that He was also pleased to make and to style Himself a servant, when He says, “Even as the Son of man came not to be ministered unto [served], but to minister [serve], and to lay down His life for many.” Every one, therefore, is the servant of Christ in the same way as Christ also is a servant. And he that serves Christ in this way will be honored by His Father with the signal honor of being with His Son, and having nothing wanting to his happiness for ever.
Source: Tractates on the Gospel of John (New Advent)