If the universe began to exist, the universe has a cause.
We can start with this being an unsupported claim. The fact is, outside the dimension of time, "began" is nonsensical, just like saying that something is north of the north pole.
The other implied claim here is also problematic, that (as it is usually written in the Kalam Cosmological Argument) whatever begins to exist has a cause. This is an inference (and argument in itself) that basically states that all the things we know of that begin to exist have a cause, therefore, all the things we don't know of the begin to exist also have a cause. This is an
hasty generalization . We can correct this by saying "therefore, all the things we don't know of the begin to exist
probably also have a cause." By doing so, we just removed the logical certainty that the arguer is going for with the deductive syllogism.
The universe began to exist.
This
begs the question . Besides the time issue mentioned previously, we only know how the universe expanded a moment after "The Big Bang" and we know nothing "before." In other words, our knowledge of the event begins with existence... something is already there.
Through the same method of induction on which the first premise relies, we can also say that everything we know of that exists is made up of other "stuff" that has already existed, therefore, what we call our universe probably is also made up of stuff that already existed. This means that the universe only began to exist in name, but the building blocks always existed. In other words, we don't have a unique act of creation; we have common instance of energy changing forms.
Therefore, the universe has a cause.
We can no longer conclude this with any level of confidence, but assuming we can...
The cause of the universe is most plausibly God.
This is a simply an assertion. In fairness to the person who made this argument, I would suspect that they are prepared to offer other arguments and lines of evidence as to why they came up with this conclusion. But as it stands now, it is simply an assertion with zero support as the premises given don't at all support this conclusion.
I am not the first to say this as this argument for God has been around for quite some time, but at best this argument can be claimed to establish that the universe has a cause. Other arguments are then needed to provide evidence that the cause is "most plausibly God".