This is one of those questions where the Holy Spirit sweetly draws us closer to scripture to ponder the question. You know? The journey to the answer is more important than the destination.
The Holy Father discusses the authorship of the gospel of John in his recent book, Jesus of Nazareth. I just re-read this section of the book last night, and that doesn’t jump out to me, that he explains those words.
I just can’t remember, but there is something special about the place that this disciple had at Jesus’ last Passover, and how he laid his head on Jesus.
That’s all I can remember. I haven’t looked in my Matthew Henry Commentary yet, to see if that author offers any explanation.
But, the Pope’s introduction to the gospel of John is a deep scripture lesson from a master. There seems to be something there about how this John was possibly the son of a temple priest. He would have been very versed in scripture, and he had not the superficial religiousity of the Pharisees, but a deep love of God from his association with the Temple.
And, this gospel is written not from the same point of view as the synoptics. A very telling section of the gospel is the following:
JOHN
1:15 * John testified to him and cried out, saying, “This was he of whom I said, ‘The one who is coming after me ranks ahead of me because he existed before me.’”
1:16 From his fullness we have all received, grace in place of grace,*
1:17 because while the law was given through Moses, grace and truth came through Jesus Christ.
1:18 No one has ever seen God. The only Son, God, * who is at the Father’s side, has revealed him.
This has John the Baptist in the text. And, he, in the evangelist John’s gospel, is comparing Jesus to Moses. the beloved disciple was so overwhelmed by Jesus, that he surely must have considered himself beloved.
This is a rational argument from the scripture. This is a disciple’s exclamation, that God loves me.