“The theistic response to Sartre is brief. First, God is not a self-caused Being; He is an uncaused Being. A self-caused Being is impossible, but an uncaused Being is not. Second, theists do not hold that every thing is caused, but only that contingent things are caused. A Necessary Being does not need a cause, since He exists by His very nature.”
The quote is from Introduction to Philosophy, A Christian Perspective by Geisler and Feinberg (pp. 293f.). As the Hebrews writer put it long ago, “For every house is built by someone, but the builder of all things is God” (3:4, ESV). God is unique in that he is the only one whose very nature is to be. Thus, God instructs Moses to tell Israel, “I AM has sent me to you” (Exod. 3:14). Everything outside God is contingent (i.e. dependent), requiring an adequate cause for its existence. “By faith we understand that the universe was created by the word of God, so that what is seen was not made out of things that are visible” (Heb. 11:3). The principle of causation leads inexorably to an infinite, uncaused, Creator. The atheist must be false to his own nature (which was made to seek God, Acts 17:27), false to the overwhelming evidence (the heavens declare God’s glory, Psalm 19:1), and false to right reason (since disbelief is inexcusable, Rom. 1:20). His is a fool’s errand.