Here’s an excellent post by J. Warner Wallace to help us understand the cosmological argument. He asks why the cause of the universe has to be God.
It’s Reasonable to Believe God Is the Uncaused, “First Cause”
Rationality dictates the ultimate cause of the universe, (even if it isn’t God), must have certain characteristics. In addition to being non-spatial, a temporal, immaterial and eternal (uncaused), it must also be powerful enough to bring everything into existence from nothing. Finally, there is good reason to believe the cause of the universe is personal. Impersonal forces cannot cause (or refuse to cause) at will. The minute an impersonal force exists, its effect is experienced. When the impersonal force of gravity is introduced into an environment, for example, its effect (the gravitational attraction) is felt immediately. If the cause of the universe is simply an impersonal force, its effect (the beginning of the universe) would occur simultaneous with its existence. In other words, the cause of the universe would only be as old as the universe itself. Yet we accept the reasonable existence of an uncaused first cause (one that is not finite like the universe it caused). For this reason, a personal force, capable of willing the beginning of the universe, is the best explanation for the first cause of the cosmos. This cause can be reasonably described as non-spatial, a temporal, immaterial, eternal, all-powerful and personal: descriptive characteristics commonly reserved for the Being we identify as God.
All of us, whether we are atheists or theists, are trying to identify the first cause of the universe. The eternal nature of this non-spatial, a temporal, immaterial cause is required in order to avoid the problem of infinite regress. It is, therefore, irrational to ask “What caused the uncaused first cause?” It is far more reasonable to simply recognize the attributes of this cause as an accurate description of God.
If you are talking about the beginning of space, the cause of the beginning of space is not itself in space.
If you are talking about the beginning of time, the cause of the beginning of time is not itself in time.
If you are talking about the beginning of matter, the cause of the beginning of matter is not itself composed of matter.
If you are talking about an event without any physical antecedent conditions to cause it in a deterministic way (e.g. – water boiling when heated), then the cause is a free choice by a free agent.
The type of effect (new universe) determines the characteristics of the cause of the effect. Whatever has these properties of being non-material, eternal and personal is not something that atheists are going to like. A cause like this has no place in their naturalistic view.