According to Osho, compassion is emphasized because only love arising from one's self-nature truly transforms. Anger drags both down and merely feeds old conditioning people can easily bear, while compassion hits deep and awakens awareness. Remaining rooted in one's being radiates a reminder for others to center themselves. Even severe Zen methods work only when they are expressions of compassion, never anger; love is the only medicine.
Love changes people because it comes from your true self and touches their heart, while anger just creates more anger.