The development of compassion is the point of the path to enlightenment, the end result: the removal of all separateness from others and the spontaneous capacity to benefit all sentient beings perfectly.
Why “courageous”? Because genuine compassion encompasses all living beings, including the harmers, the negative ones, not just the innocent victims.
But as His Holiness the Dalai Lama says, “Compassion is not enough: we need wisdom.” Without the development of renunciation of suffering and its causes (which comes from understanding of the law of karma and the workings of one’s own mind) and of the wisdom that sees reality as it is (which comes from understanding dependent arising and emptiness) one cannot fully develop such radical compassion.
The great bodhisattvas are fierce in their determination to never give up on sentient beings: they “think in terms of eons,” as His Holiness the Dalai Lama says.