Knowing is believing
"... since what may be known about God is plain to them, because God has made it plain to them." Romans 1.19
Theologians like Martin Buber and John Baillie insist that God is known on his own terms, through personal relationship, not as a concept devised by philosophers and soothsayers. They champion the "experiential argument" for the existence of God, namely that it is the intimacy of our relating to God that his existence is confirmed to us personally.
Needless to say that is not convincing for those who have not experienced the divine presence but are interested in the possibility and indeed the plausibility of such an encounter. So other theologians such as Schubert Ogden and Hans Kung developed the "existential argument" which is similar but more objective. Their claim is that human existence depends on the reality of God which, once embraced, makes sense of everything including the extraordinary tenacity with which all creatures cling to life.
Theism versus a-theism: deny God and life is meaningless; take that step of faith and, like a kaleidoscope, life assumes a clarity, richness, purpose and beauty which point inexorably to the genius and therefore to the presence of its Creator. Yet, as with the experiential argument, the existential argument requires the exercise of personal trust and does not establish objective fact.