The Christian claims that God created ex nihilo (out of nothing) by which the Christian minimally means that there was no material cause of the world’s coming into existence, even if God was its efficient cause.
Some people, including Christians, have difficulty here because to their minds matter is conceived of to be a thing which can neither be created nor destroyed. They have thus been inclined to think that the Christian claim that God created out of nothing is unintelligible. However, I think this is a good argument, at least for a Christian, to think that they are misconceiving matter itself. If what some person S means by matter is something which cannot possibly be created, and if the Christian claims that God created matter, and if the Christian believes that it is not and cannot be contradictory to say that God created the world, then what the Christian means by matter just isn’t what S means by matter.
What, then, is matter? I think the only ways to account for matter as a thing which could have been created are going to wind up being phenomenalist (like Leibniz) or idealist (like Berkeley) accounts of it. But there you have it – it will mean the Christian should be a phenomenalist or an idealist, rather than adopt an old-line ‘materialist’ view of matter.