Why is there something rather than nothing?
Reason demands that if anything is, there must be some source. Otherwise there would be nothing. Unless something (someone) has always existed in itself (himself), nothing could possibly exist at all.
God exists in Himself eternally. Only because He is the Self-existent is all other existence apart from Him possible.
“For by Him all things were created, both in the heavens and on the earth, visible and invisible, . . . all things have been created through Him (the Son) and for Him. He is before all things, and in Him all things hold together” (Col 1:16-17)..
Why must reason demand that “someone” like this exists, and not just that “something” like this exists?
(Spotlight 3, Lesson 2 in Doctrine 101: Learning about God)