Why does the First Cause for the existence of the Universe has to be a spiritual entity? Why can't it be material in nature?

 The consideration that led us to seek a first cause also lead to the consideration that the first cause is immaterial. Consider the properties of matter:

Composition: matter is something composed of parts, and every part is external to the other parts. Matter is parts outside parts. The first cause must be simple or incomposite; otherwise, we would have to seek the cause of the unity of the first cause, in which case it would not be ‘first’.

Potentiality-Actuality: This is a consideration from the Aristotelian framework. Matter is something indeterminate and is something determinate (capable of being referred to as a this-x) because of the presence of a Form. For Aristotle, the first cause must be something actual, or it would not be the first cause of motion. The idea is that if everything were merely in potency to another, then there would be no motion. If the First Cause were in potency in relation to another, it would require another cause to explain its motion.

Space-Time: Anything material is located in space-time; here, the argument is similar to the argument from the compositionality of matter, except that we are concluding based on temporal and spatial parts.

Matter cannot explain self-consciousness: Since matter is parts extra partes extra partes, it cannot explain the phenomena of self-consciousness. In a materialistic world-view, self-consciousness is explained thus - X1 is an informational brain state, X2 is an informational brain state about X1, and X1 is not identical to X2, though some kind of intimate relation may be posited between the two. Here, every brain state is directed at something else, but no brain state reflects upon itself or reports itself. This leads to an infinite regress that can be explained through an analogy: if I hire one spy to monitor the movements of someone else and then a second spy to monitor the first spy, then there is going to be an infinite regress of spies. Self-Consciousness is possible only if X1 = X2, or the consciousness of x and the consciousness of the consciousness of x are identical.

The basic idea is that the explanans must be ontologically distinct from the explanandum, or it can do no explaining. Nothing material can explain something material. The principle of causal closure asserts that one material thing is the necessary and sufficient condition for the existence of another. In this world-view, it is only a necessary, not a sufficient condition.

But even if immaterial, why must the first cause be intellectual? Here, ‘intellect ’ and ‘pure thought’ refer to self-consciousness. Some, like Neo-Platonists, believe that the first principle - the One, is beyond intellect because self-consciousness, even though it has the highest amount of unity compared to anything material, is still not absolutely simple. The reason is that within self-consciousness, the subject is both the subject and the object of consciousness, and to be its own object requires some internal difference from itself. It is identity-difference, but not simple identity. The One is absolutely simple and can only be referred to in negative terms. Others, such as Advaita Vedanta and Sankhya, also do not regard self-consciousness as the first principle and hence believe in pure consciousness, i.e. a consciousness which is always a seer, never the seen.

Aristotle, followed by medieval scholastic theologians and, much later, Leibniz and Hegel, considers self-consciousness to be absolutely simple and hence the first cause. Pure self-identity, as the above philosophical schools consider it, is an abstraction, and intellect can be both self-conscious and simple at the same time. My own sympathies are with the latter point of view, specifically that of Hegel’s. The basic idea is that the first principle must have the highest amount of unity, while everything else has this unity borrowed from the first principle (hence the latter is absolutely simple and the former is not). Nothing material can fit the bill. Intellect or self-consciousness fulfils these criteria and is a good candidate for the first cause. Despite disagreement about the issue, the first cause has to be taken as something immaterial is certain. On the other hand, for materialism, there is no first cause, and the issue hinges on the explanatory value of matter to explain matter.