The Cosmological Argument: Three Key Points
The cosmological argument comes down to three simple ideas that St Thomas Aquinas developed centuries ago. First, if something's moving or changing, something else must have caused that movement - leading us to an Unmoved Mover (God). Second, every effect needs a cause, and you can't have an endless chain of causes, so there must be a First Cause.
The third argument focuses on contingent beings - things that exist but could just as easily not exist (like you, me, and everything around us). These contingent things depend on something else for their existence, and there can't be an infinite chain of dependent things.
This means there must be a necessary being - something that has to exist and doesn't depend on anything else. According to Aquinas, that's God.
Quick Check: Think of dominoes falling - each one knocks over the next, but something had to push the first domino!