(1) All contingencies require necessities to ground them.
(2) All natural things are contingent
(3) the universe is natural, therefore, the universe is contingent
(4) the universe requires a necessity upon which its existence is grounded, Therefore, the origin of the universe must be necessary.
(5)Since the origin of the universe must be necessary (from 2,4 and 5) and not contingent the origin cannot have a cause.
(6)The origin of universe is necessary and must be eternal and first cause, since this is the definition of God (see Rational Warrant page) then the origin of the universe must be God.