Why is it so important for believers to affirm that in creating all that is God does not work with or use anything at all—nothing, that is, other than his own omnipotence? When the doctrine of creation out-of-nothing was being formulated in the early Church, it seemed obvious to the Church Fathers that the opening of Genesis stood out in stark contrast to the prevailing philosophical and scientific view that the universe is eternal. A Platonic Demiurge, for example, or an Aristotelian Unmoved Mover, would work with already existing stuff to bring order and/or motion to the world. Such a god would not be the complete cause of all that is, would not be the sovereign Lord of the universe. To emphasize that God, revealed in the Bible, was such a complete cause of existence meant that creation had to be “out of nothing.” What this meant was that God did not use anything at all—no pre-existent matter, no primal chaos—in his creative act.
For the Church Fathers, creation out-of-nothing also countered any temptation to think that matter was evil and not created by God. All that is comes from God, and all that is, is good. There are not, as the Manicheans thought, two first principles, one supremely good, the other supremely evil. Systematic reflection in the Christian tradition (and in Jewish and Muslim traditions as well) on what it means for God to create involved difficult questions about the intelligibility of something’s coming from nothing, given the fundamental premise that it is not possible to get something from nothing. It also involved discussions about the relationship between a created universe, generally identified as one that is temporally finite (i.e., with a beginning), and the well-established scientific view that the universe is eternal. It would not be until the 13th century that the doctrine of creation would find its fullest expression (and its most able defender) in Thomas Aquinas.
For Thomas, God’s act of creating the universe is not primarily some distant event. Creation is the on-going, complete causing of all that is. To be created means to have a relationship of complete dependency, of everything that one is, upon God as cause.