If a being created existence out of nothing, can that being be part of the existence it created, or must it have been part of the nothing, and therefore not have existed?
If this being was after all something and not nothing, who or what created it? And if it didn't need creating, why does the rest of existence need creating?
Theists like to explain that the difference between God and the rest of existence is that God is a "necessary being" while the rest of existence is "contingent".
Contingent refers to existence that interacts in a causal chain with other existence. A creates B and B creates C and C creates D in this interaction of cause and effect. Thus A, B, C and D are "contingent". But if A is contingent then something must have created A. But if A is God, then nothing created A. The causal chain is broken by saying that A is a "necessary" being which means, simply, uncaused. But is this anything other than a word game?
There are two problems. The first is that causality is a two-way street. Effects have causes, but those causes have to be the sort of thing than can make those effect happen. Causality, in short, is an interaction. Which means that for God to be capable of interacting with the physical world in a way which enables God to create and move things, God must be contingent or have some contingent components. Declaring God "necessary" is simply a raw fiat.
The above objection can be put in other terms. Time is a function of change--if there were no change there would be and could be no time. Time in fact is only a way of measuring change by a standard clock--that is, by something that changes in a extremely regular way. This is why God is defined as unchanging and as the creator of our world as a world of change. But how can the unchanging create anything or start anything moving, since it much change to do so. This is why we say that contingency and causality are two-way streets. It means that either God is also contingent, or God is out of the creation business. If God is not the creator then God is not really God as we mean the term. On the other hand, if God is contingent, then God cannot be the first cause in a chain.
The second objection is even more interesting. It's based on the observation that causality--and thus contingency--is actually nothing but a mental construct and not in fact a description of how existence actually is. For our thoughts to be useful, we have to think about the world in terms of causes and effects, but causality is part of the currency of human thought--not an aspect of existence itself.