4 And who, besides, would not be disposed, in the case of these two apostles, Peter and John, to make this further inquiry, why the Lord loved John better, when He Himself was better loved by Peter? For wherever John has something to say of himself, in order that the reference may be understood without any mention of his name, he adds this, that Jesus loved him, as if he were the only one so loved, that he might be distinguished by this mark from the others, who were all of them certainly loved by Christ: and what else, when he so spoke, did he wish to be understood but that he himself was more abundantly loved?
And far be it that he should utter a falsehood. And what greater proof could Jesus have given of His own greater love to him than that this man, who was only a partner with the rest of his fellow disciples in the great salvation, should be the only one that leaned on the breast of the Saviour Himself? And further, that the Apostle Peter loved Christ more than the others, may be adduced from many documentary evidences; but to go no further after others, it is plainly enough apparent in the lesson almost immediately preceding the present, in connection with that third manifestation of the Lord, when He put to him the question, “Do you love me more than these?”
He knew it, of course, and yet asked, in order that we also, who read the Gospel, might know Peter's love to Christ, both from the questions of the One and the answers of the other. But when Peter only replied, “I love You,” without adding, “more than these,” his answer contained all that he knew of himself. For he could not know how much He was loved by any other, not being able to look into that other's heart. But by saying in the earliest of his answers, “Yea, Lord, You know,” he stated in clear enough terms, that it was with perfect knowledge of all that the Lord asked what He asked.
The Lord therefore knew, not only that Peter loved Him, but also that he loved Him more than the others. And yet if we propose to ourselves, in the way of inquiry, which of the two is the better, he that loves Christ more or he that loves Him less, who will hesitate to answer, he is the better that loves Him more? If, on the other hand, we propose this question, which of the two is the better, he that is loved less or he that is loved more by Christ, without any doubt we shall reply that he is the better who is loved the more by Christ.
In the comparison therefore which I drew first, Peter is superior to John; but in the latter, John is preferred to Peter. Accordingly, we have a third to propose in this form: Which of the two disciples is the better, he that loves Christ less than his fellow disciple [does], and is loved more than his fellow disciple by Christ? Or he who is loved less than his fellow disciple by Christ, while he, more than his fellow disciple, loves Christ? Here it is that the answer plainly halts, and the question grows in magnitude.
As far, however, as my own wisdom goes, I might easily reply, that he is the better who loves Christ the more, but he the happier who is loved the more by Christ; if only I could thoroughly see how to defend the justice of our Deliverer in loving him the less by whom He is loved the more, and him the more by whom He is loved the less.
Source: Tractates on the Gospel of John (New Advent)