Whatever we do as our practices, it is necessary to have the motivation of universal compassion, or bodhicitta. One of the more important reasons is that our yearning for happiness and well being is shared by all sentient beings. The reason why we haven't achieved enlightenment is our self grasping attitude, which binds us to samsara. Cultivating compassion is a direct antidote to self grasping. The Buddha taught 84,000 teachings to eliminate 84,000 emotional attachments. But all of them can be traced back to the self cherishing attitude. The direct antidotes to this are the understanding of emptiness and the practice of compassion.
http://medicinebuddhasangha.org/teachings/moonbeams_mahamudra.html