Naturalistic Theism: Cosmological Proofs II
...Whence, farther, it is also evident, Secondly, that some being was uncaused, or was ever of itself without any cause. For what never was from another had never any cause, since nothing could be its own cause. And somewhat, as appears from what hath been said never was from another. Or it may be plainly argued thus; that either some being was uncaused, or all being was caused. But if all being was caused, then some one at least was the cause of itself; which hath been already shown impossible. Therefore the expression commonly used concerning the first being, that it was of itself, is only to be taken negatively, that is that it was not another; not positively, as if it did some time make itself. Or what there is positive signified by that form of speech, is only to be taken thus, that it was a being of that nature, as that it was impossible it should ever not have been; not that it did ever of itself step out of not being into being.
To sum up: whatever was eternal was uncaused, or existed without cause. Since what was first cannot be its own cause, something is eternal. We take this then negatively only, that what was first is not of another.
...And now is hence farther evident, thirdly, that some being is independent upon any other, that is whereas it already appears that some being did never depend on any other, as a productive cause, and was not beholden to any other, this it might come into being; it is thereupon equally evident that it is simply independent, or cannot beholden to any for its continued being. For what did never need a productive cause, doth as little need a sustaining or conserving cause. And to make this more plain, either some being in independent, or all being is dependent. But there is nothing without the compass of all being whereon it may depend. Wherefore to say, that all being doth depend, is to say it depends on nothing, that is that it depends not. For to depend on nothing, is not to depend. It is therefore a manifest contradiction to say that all being doth depend; against which it is no relief to urge, that all beings do circularly depend on one another. For so, however the whole circle or sphere of being should depend on nothing; or one at last depend on itself, which negatively taken, as before, is true, and the thing we contend for—that one, the common spport of all the rest, depends not on any thing without itself.—[John Howe, (1630-1705)]
Again to summarize: Since what was first is not of another it is not dependent upon another, but self-sustaining. It then follows that either what is first is independent or all is dependent. Since all cannot be dependent else it depends on nothing, what was first is independent and all else dependent upon that which was first.