Modern (secular) science tends to see things in terms of an infinite regress - but this is implicit, demonstrated by how scientists behave and not by their expressed beliefs.
Infinite regress means that A was caused by B which was caused by C - and so on forever.
This is very much a linear and causal view - linear causality is the primary metaphysical assumption about the nature of reality.
This is of course paradoxical, since if there were an infinite number of previous causes, then it would take eternity for them to operate - so nothing could ever be caused.
However, all ultimate explanations are paradoxical - so it is not as if there was any non-paradoxical alternative.
Mind of God
Mainstream Christan theology takes the (ultimately Platonic) attitude that the ultimate explanation is the mind of God - God's will, God's decision.
This is regarded as inexplicable, because in this conception of God He is omnipotent, omniscient, omnipresent - causes everything and thus sustains the universe, and is free of all passions, impassive, unchanging - yet, somehow, Loves us and we are supposed to Love (as well as worship) Him.
(To worship and fear such a concept of God is easy; to Love Him and believe He Loves us - especially given that He is directly responsible for - wills - absolutely everything that happens... well that is not so easy.)
So asking about the ultimate cause of A may be followed by B and C but does not go on forever - sooner or later the causes come to terminus in the mind of God, in the uncaused direct will and action of God.
For this view, everything is necessary - absolutely everything.
Nothing could be other than as it is.
(Which leaves no space, not one Angstrom of space, for real, actual, free will. So Christianity is impossible...)
But this is not really an explanation - rather it is a limit to explanation. A stop sign.
So there is a paradoxical quality about using the mind of God as the ultimate explanation - especially for a Christian.
It just is
But there is another alternative, seldom given much attention but in fact the one to which I adhere; and which is the pluralist alternative; and it is like the mind of God explanation except that ALL causal pathways do NOT return to the mind of God, but some of them terminate in 'It Just Is'.
So some 'A's do have a line of causality leading back to the mind of God (to God's uncaused will and action). But other A, B, C sequences terminate in the assumption that that Just Is 'how things are' and presumably 'always have been' - in other words the nature of reality.
Therefore, two classes of explanation: two types of ultimate cause - God, and It Just Is...
(Implying a reality which contains God, rather than being contained-by God).
On this view, some things are ultimately caused by God, and other things are not.
(Some things are Good, and other things are not - either being neutral, such as forces and laws of nature and substance; or evil, which means anti-Good, destructive of Good.)
Reality is therefore not ultimately a harmony or stasis; but instead some kind of dynamic conflict or process, between ultimate realities, ultimate causes (of which God is one); there is 'opposition in all things'.
Another way to contrast the mind of God from It Just Is, is to consider the origin of Forms.
Most philosophical and scientific analyses necessarily assume forms are real, and lie behind appearances. This applies to Plato and even more to Aristotle, to Thomism, is a recurrent and continuous feature of science (especially biology), and has reappeared in our time in the work of Rupert Sheldrake.
(The modern theory of evolution by natural selection depends utterly on assumptions about form, but its flaw is that it cannot see this, and denies and ridicules such discourse. Hence form is an unexamined assumption of natural selection, shaping all discourse but opaque to perception.)
But where do the forms come from?
The two answers are essentially: 1. They are present in, and a decision of, the mind of God (Aristotle, Aquinas); or 2. They Just Are (which has been the implicit view of most scientists interested in form, including Sheldrake.)
But how do we know about forms, how do we know how many there are and their characteristics, how can we detect a form or decide what form applies in a particular situation?
If forms come from the mind of God then we can assume God plants the necessary knowledge in our own minds (the view of Aristotle and Aquinas).
But if forms Just Are, then how would we know about them? And how could disputes about form be settled (even in theory) when there was any disagreement about the number, nature, identity, characteristics of form?
For the Just Is understanding, the implication is that we know about things like form partly by them being built-into us, by necessity - since these things are ultimate causes; partly by revelation from God.
But then how does God know?
I think the implication is that God must himself be a kind of philosopher and historian and scientist.
He is Himself one of the ultimate realities - but knows about the other ultimate realities only conjecturally; in terms of unrefuted hypotheses that seem to work.
So, God created (shaped, ordered) the universe, and knows what it is to work-with the ultimate realities - but He does not (on this view) know their number and nature directly or for certain.
He knows far, far, far better than we do what are the nature of the ultimate realities (perhaps matter, and the forces and laws of the universe, and the ultimate forms), because of his vastly greater (to put it mildly!) experience; but He does not know in the way a God who is himself everything would know about what went on inside himself.
The infinite regress view is respectable among scientists, and the God's mind view is respectable among philosophers and mainstream among Christian theologians - both are respectable despite having big, big, BIG paradoxes and problems.
So also does It Just Is have paradoxes and problems. But It Just Is does have has the BIG advantages (for a Christian) of leaving space for real free will, and also distinguishing between the ultimate origins of Good and evil.
But, at any rate, some people - and I am one, and many tribal peoples and probably most children are others, are apparently satisfied to stop asking for further explanations when they reach something they can believe Just Is...
...The universe has always been, it has always had this stuff in it, the stuff has always operated and reacted and moved in this way and by these rules; God has always been, and we humans have always been and we always will be (some kind of thread of consciousness extending back in time forever, perhaps very thin at times but never severed, always continuous) - But we have changed; and we continue to change, according to the constraints of the stuff and the rules and in love and obedience to God; who, as Father and of his Goodness, shaped us and gave us self-awareness, personhood, godhood; all ultimately because we Just Are, God Just Is, and we and God lived and live among many other things that Just Are.