Too clever by half
"In them is fulfilled the prophecy of Isaiah: "'You will be ever hearing but never understanding; you will be ever seeing but never perceiving." Matthew 13.14
Of all the arguments in support of faith in the existence of God, surely the most unique, intriguing and ingenious is the "ontological argument"? Credit goes to Anselm and his definition of God as "that than which nothing greater can be conceived." And if we concede that existence is greater than non-existence (the pound coin in your hand being superior to the one that isn't there), then - for a proper appreciation of God - he must exist!
Other big names to have flocked to Anselm's cause include Rene Descartes, Gottfried Leibniz, Charles Hartshorne and Alvin Plantinga. An impressive list, yet still not convincing enough for those who question whether "existence" can be claimed as a "quality" in the same way as the other attributes of the One "than which nothing greater can be conceived". This becomes the "achilles heel" of the ontological argument.
But what if we were put put all of the arguments for the existence of God together? That is what proponents of the "cumulative argument" have done, claiming that their sheer scope renders the probability of their basic tenet (God's existence) is overwhelming. But not if you require certainty rather than probability! And though believers claim "assurance of faith", that is a personal matter and will not apply to the sceptic who is looking for objective proof.
So we are thrown back on the reality that belief in God is a matter of faith. Only those with the eyes to "see" will perceive God. Does this render evangelism a fruitless task, then? Not necessarily. Because if God does exists, then it is in his gift to "open" those eyes and why shouldn't he choose to do that through evangelism - as well as direct revelation or whatever other means he may choose?