John Lightfoot on Mark 10:21

[Loved him.] That is, he manifested by some outward gesture that this man pleased him, both in his question and in his answer: when he both seriously inquired concerning attaining eternal life; and seriously professed that he had addicted himself to God's commandments with all care and circumspection.

Let us compare the customs of the Masters among the Jews: Eliezer Ben Erech obtained leave from Rabban Jochanan Ben Zaccai to discourse of some things before him. He discoursed of Ezekiel's chariot (chapter 1), or, of mystical divinity. "When he had made an end, Rabban Jochanan arose up, and kissed his head." "R. Abba Bar Cahna heard R. Levi disputing profoundly. When he had made an end, R. Abba rose up and kissed his head." There is a story of a certain Nazarite young man that exceedingly pleased Simeon the Just with a certain answer that he gave. Whereupon, said Simeon, "I bowed towards him with my head, and said, O son, let such as you be multiplied in Israel." The story is found elsewhere, where for I bowed towards him with my head, it is I embraced him and kissed his head. "Miriam, before the birth of Moses, had prophesied, My mother shall bring forth a son who shall deliver Israel. When he was born the whole house was filled with light. His father stood forth, and kissed her upon the head, and said, Thy prophecy is fulfilled. And when they cast him into the river, he struck her upon the head."

What if our Saviour used this very gesture towards this young man? And that the more conveniently, when he was now upon his knees before him. Some gesture, at least, he used, whereby it appeared, both to the young man and to the standers-by, that the young man did not a little please him, both by his question and by his answer. So I have loved, Psalm 116:1, in the LXX, I have loved, one may render well, it pleaseth me well. So Josephus of David's soldiers, (1 Sam 30:22): "Those four hundred who went to the battle would not impart the spoils to the two hundred who were faint and weary; and said, That they should 'love' [that is, be well pleased] that they had received their wives safe again."

In some parity of sense, John is called the disciple, whom Jesus loved; not that Jesus loved him more than the rest with his eternal, infinite, saving love, but he favoured him more with some outward kindness and more intimate friendship and familiarity. And why? Because John had promised that he would take care of Christ's mother after his death. For those words of our Saviour upon the cross to John, 'Behold thy mother!' and to his mother, 'Behold thy son!' and that from thence John took her home, do carry a fair probability with them, that that was not the first time that John heard of such a matter, but that long before he had so promised.

I have loved thee, Isaiah 60:10, is the rendering of I have had pity upon thee: which may here also agree very well, "Jesus had pity upon him."