In many of the Mahayana Sutras, there are long lists of bodhisattvas. In Zen, there are really only two: Manjusri, the bodhisattva of wisdom, and Kanzeon, the bodhisattva of compassion.
Manjusri is generally the figure on the zen altar. He sits on top of a lion and wields a sword, to cut delusion. “Wisdom” is a misleading translation of prajna, which literally means ‘pre-knowledge’: that state of wholeness before we cut the world into pieces, either through language or adherence to a self. For this reason, his sword is unusual. He cuts the world into one.
We can see him as a description of one aspect of zazen, and if we can, we can then see Kanzeon as another, and the two of them as Not-Two.
Kanzeon is normally represented as having a large number of hands and eyes. The symbology is her capacity to see the suffering of living beings, and to assist them, but I think this multitude of hands and eyes is also descriptive of our state in zazen.
Manjusri is a definite figure, but, for Dogen at least, Kanzeon is equated with the whole of existence. In our dualistic way of thinking, the world is divided up into things, which then interact, but if we cast this aside, and de-centre this I/eye, we enter into the vast compassionate space which can hold the experience and perspectives of all beings (eyes) and the expression of those beings (hands). We are not cultivating compassion. It is cultivating us.
On this basis, we can then see why it is Kanzeon (compassion) practicing zazen in The Heart Sutra, which we chant after sitting, and why she is, as it were, practicing Manjusri (prajna), and vice-versa, and we can reconfigure the Heart Sutra as a poetic re-expression of the zazen which we have just experienced. Not just poetic, obviously.