The same line of reasoning clearly shows that God necessarily exists. For everything that has the possibility of being and of not being, is mutable. But God is absolutely immutable, as has been demonstrated. Therefore it is impossible for God to be and not to be. But anything that exists in such a way that it is impossible for it not to exist, is necessarily Being itself, ipsum esse. Necessary existence, and impossibility of nonexistence, mean one and the same thing. Therefore God must necessarily exist.
Moreover, everything that has a possibility of being and of not being, needs something else to make it be, for, as far as it itself is concerned, it is indifferent with regard to either alternative. But that which causes another thing to be, is prior to that thing. Hence something exists prior to that which has the possibility of being and of not being. However, nothing is prior to God. Therefore it is impossible for Him to be and not to be; of necessity, He must be. And since there are some necessary things that have a cause of their necessity, a cause that must be prior to them, God, who is the first of all, has no cause of His own necessity. Therefore it is necessary for God to be through Himself.
St. Thomas Aquinas. (1265-1274). Compendium Theologiae: Necessity of God’s Existence, trans. by Cyril Vollert. St. Louis & London: B. Herder Book Co., 1947
All scripture is given by inspiration of God and is profitable for doctrine, reproof, correction, and instruction in righteousness (2 Timothy 3:16).