Loving-kindness is like the soil into which we put the seed. Compassion is like the water and the fertiliser which we put in the soil, allowing the plant to grow. Bodhicitta is like the plant itself, like the tree of enlightenment (the bodhi tree). And so, this "bodhi tree" of the bodhisattva attitude is planted in the soil of loving-kindness and watered and fertilised with compassion. Then it grows greater and greater until it finally produces its fruit, which benefits all living beings. This fruit is the three bodies of a Buddha - two form bodies and one formless body.

-- Phagmo Drupa Dorje Gyalpo