For when it is said, for example, that the brazen serpent was the ‘type’ of Christ, something is explained, to be sure, but not everything; in particular, it has not been said precisely why the serpent and not some other animal has been chosen to be this ‘type’, which is the essential point. Typology therefore needs to be deepened and explained by symbolism: the type needs to be considered not only in its biblical context, but also in its universal usage and meaning.
…We easily observe that the trees of the brazen serpent and the cross, each bearing the good serpent, are inverse images of the tree of the earthly Paradise, bearing the evil serpent.
From Divine Craftsmanship by Jean Hani (21).