This argument relies on sufficient reason, there has to be a reason why everything around us exists. What is needed is an unmoved-mover, someone who is unattached to the web of contingency. .
The arguments presented by Plato gave the theist belief that the cosmological arguments are still hopeful. Plato's arguments are based on the obvious, such as every day we observe things moving. Another either moves things that move or they are self-moved. If they are self-moved then they must be eternal. Within this argument for a first cause, Plato's self-mover is God. This argument can be questioned by asking: When the wind blows the door shut, do we believe God was the cause? I doubt it, since the scientific knowledge we posses today explains the forces of the wind. Although, Hume brings up a valid argument for this concept, if Plato can't conceive the thought that things with movement don't necessarily have a mover, and not all effects have causes, then they should accept that God might have a cause as well, like the universe. Now like Plato I agree that stopping at God is an arbitrary decision. However, I do not agree with Hume's argument, because it is illogical for there to be an infinite regress of causes. .
Although, we can look at these arguments from a different angle by using Thomas Aquinas's "five ways", which he argues for the existence of God. The first three arguments are dependent on the principal that infinite regresses of causes are inconceivable, which means they rely on the "first cause". His first way is motion, which to Aquinas is going from a potential state to an actual state. .
This process of actualizing the potential of other things has to have a higher ground, so there must be an unmoved-mover. The second way is that in nature we see that one event, is caused by another. The argument here is that this cannot be a set of infinite causes, there has to be a first cause.