Naturally, before cultivating great compassion, one should generate renunciation first. Once cannot have great compassion for sentient beings if one is unaware of the suffering of samsara, because for sentient beings if one is unaware of the suffering of samsara, because compassion comes from the suffering of sentient beings. No compassion, no bodhicitta either. The other condition for developing renunciation is the desire for liberation. When seeing the suffering of sentient beings, one aspires to save them from the clutches of samsara forever. But on second thought, how can one help others if one cannot attain liberation for oneself in the first place ? With this in mind, the two requisites for generating renunciation - aversion to samsara and desire for liberation - are complete. 

~Depicted from From Believers to Boddhisattvas