I have long felt that as a Mahayana school Zen is all about compassion-but since the Chinese monks who developed the tradition's style assumed compassion teachings and didn't feel they had to emphasize them, Zen literature contains only a few explicit teachings on compassion. So Western Zen practitioners need a remedial course, and lojong brilliantly fills the bill.
"A New Perspective on an Ancient Practice: An Interview with Zoketsu Norman Fischer," Shambhala Publications, Jan 8, 2013.