The Bible asserts that there exists a supreme Being. In the Bible, this supreme Being is given the title of God.
(Out of reverence, I choose to fully capitalize the title as GOD. This serves as a personal reminder to elevate God in my thinking.)
Certain Scriptures, such as Hebrews 11:6, directly affirm the existence of GOD.
6 And without faith it is impossible to please God, because anyone who comes to him must believe that he exists and that he rewards those who earnestly seek him.Hebrews 11:6 NIV
The first verse of the Bible affirms the existence of GOD:
1 In the beginning God made heaven and earth.Genesis 1:1 OSB
While the Bible does affirm GOD’s existence, it is not the focus of Scripture to lay out a comprehensive case for the existence of GOD. To be sure, a compelling case may be made from the Scriptures, but the writings that comprise the Bible were written at a time where most (but not all) people believed in supernatural gods.
Therefore, Scripture generally assumes that the reader believes GOD is real.
As the psalmist wrote:
1 The fool says in his heart, “There is no God.”Psalm 13 :1b OSB