Material was seen as having spiritual values, and existed within God's creation. Contemporary views discard these notions of meanings within materials, and the possibility of God having any relation to material. The question of understanding material outside of creation is a foreign notion, and my question is not a question the medieval mind would ask.
Theologian St. Thomas Aquinas is the definitive voice of medieval thought. His synthesis of prevailing cosmologies and doctrines of the 12th century is the apex of Gothic thinking. To understand how the medieval mind understood material, we turn to Thomistic doctrine.
To understand material from within a created cosmos, we have to understand it in relation to form, beauty, and God. Material, form, beauty, and God are part of an intricate ontological hierarchy.
Material is the potential of something. Material shares its etymological root with "mother". It has the potential to give life, but does not necessarily live itself.
To understand how material gives life, we must understand form. Form is a structure or pattern that is materially at one with the object. Form is something in virtue of which an object lives and is what it is. Form is the thing being itself, but possesses reality and character only in virtue of being materialised in the object.
It is important to realise that form cannot exist nor have any reality if it is not individuated in matter. Form and matter are inseparable from within the hierarchy.
Beauty and form are related ontologically within the hierarchy. Beauty is co-extensive with being; but a thing has being insofar as it actualizes a rational structure that "informs" the material. Each part of the hierarchy, material, form, and beauty, are intimately bound despite the unique disparate character of each.
Beauty, which is hierarchically below God, exists only insofar as material is realized in form, and form is the thing organized by the potential of the material.
It is important to realize that the intention of the artist does not hold a place within the hierarchy. What things are is ultimately determined by God.