When, in the Mahayana, one goes for refuge, one cultivates an unbearably powerful compassion for beings, who have been one’s mothers in the past and whose number is as boundless as the sky is vast. But it is not enough to feel compassion for them; one must be determined and decide to liberate them from their suffering. As long as one is not free oneself, however, one is powerless to bring others to freedom. Consequently, in order to free oneself and others from the perils of both samsaric existence and the peace of nirvana, one takes refuge in the Three Jewels, according to the Mahayana, until one gains enlightenment.
From The Nectar of Manjushri’s Speech,by Kunzang Pelden, page 84.