Anything which comes into existence must
have a cause. Anything which doesn't come into existence, but instead is timeless, can't
have a cause.
I would hope that's easily understood and wouldn't need further elaboration.
The problem is, big bang cosmology says that our universe had a beginning, thus it must
have a cause; a reason for that beginning.
God-denialists, realizing the theistic implications of a cause bringing our universe into existence in an unfathomably small fraction-of-a-second, have now resorted to the multiverse. Their obvious motivations are to delude themselves into believing that nature is infinite and eternal, despite our universe's apparent beginning. This, of course, means that they can avoid having to explain its (our universe's) existence. It's just the "cosmic debris" of the multiverse; an offshoot which coincidentally has life-sustaining properties, as well as a perfectly comprehensible structure perfect for discovery (science), which can be pieced together to create technology and all of our other advancements.
It's all one happy cosmic accident made possible by our glorious uncreated multiverse and Her infinite nature.
Let us all bow down and worship our purposeless creator!