The ontological argument is a philosophical argument for the existence of God that uses ontology—the state of being or existing. The ontological argument remains a tenuous argument for the existence of God. It is certainly not strong evidence for the truth of Christianity.
The classical ontological argument, proposed by St. Anselm of Canterbury in 1078 CE in his work "Proslogion," attempts to prove God's existence through reasoning alone.
Immanuel Kant, paraphrased from "Critique of Pure Reason" (1781)