Louis Jacobs, We Have Reason to Believe, pp. 25-26, 28-30:
Since Kant, these proofs [of God's existence] have been heavily assailed. The cosmological proof is held to be inadequate because it does not really explain that which it sets out to do. The difficulty of how the first cause came into being is no less if God is postulated as the Cause. Little children, with the perspicacity of innocence, often ask: 'Who made God?' The ontological proof is unsound because it is possible for the human mind to have in it the idea of a mythical creature such as a unicorn or a griffon, and no one would argue that because of this these creatures must actually exist. Finally, the teleological proof is attacked on the grounds that the evidence from design is ambiguous; if design is used as proof of the existence of a Supremely Good and Omnipotent Being, what of faulty or even positively evil design evident in the universe?...
Many theologians, nowadays, accept the validity of these refutations and admit that there can be no proof of God in the sense that there can be no proof of a mathematical formula... But they go on to remark that we can be convinced of a thing beyond of a shadow of a doubt by means other than that of mathematical proof. There is no such proof, for instance, of the existence of other human beings beside ourselves, yet we are convinced that they do exist... In other words a distinction must be drawn between proof and conviction--proof is one of the ways to conviction but there are other ways, too...
Many have arrived at this conviction as the result of a personal experience which convinces them that God exists. These men would rule out of court the very discussion of whether God exists, for, they would say, if a man is truly in love he does not ask himself if he is in love. The experience of God's Presence is sufficient...
Other thinkers, again, hold that though each of the traditional proofs in itself is unconvincing, taken together they are convincing... Granted that the proofs carry no weight as evidence, they are indications and as such have the power of supplementing each other...
What it all amounts to is this, that while the existence of God cannot be proved if we start from the beginning, none of us do, in fact, start from the beginning. We are presented with two alternative beliefs about the ultimate reality and we have to choose between them. According to one view God exists--it is He Who created us, Who fashioned our minds and implanted the moral sense within us so that we are capable of recognising beauty, truth and goodness and fighting ugliness, falsehood and evil. In this view the difficulty is how to account for the existence of evil. According to the other view there is no God... In this view the difficulties are how mind came from matter, how life emerged where there was no life before, how the universe itself came into being, how the good is possible of realisation and how man came to strive for it--how man as a tiny part of the universe came to pass judgment on it?