Today is also the feast of St Anselm. I can be a little slow, so I've never really grasped the so-called Ontological Argument, but I highly recommend an attentive reading of his Cur Deus homo - translated here in two PDF files.
I suspect that St Anselm doesn't get a fair hearing these days - his masterly exposition of the theology of Satisfaction is frequently confused with Protestant Substitution theories. (I also suspect that his 'juridical' interpretation of the Redemption has more scriptural and patristic support than his critics might concede.) Additionally, he's sometimes accused of being a rationalist - although if one takes the opening paragraphs of Cur Deus homo seriously, he's quite clear that reason does not at all supplant faith or grace. Rather, the possession of theological truths by means of reason should be understood as subsequent, supplementary and complementary to their acceptance by faith. Our faith is rational - so a grace-enlivened reason may understand the logic of what we believe and thereby grasp more profitably the truths of the faith. Reason deepens our faith rather than replaces it.