The Ontological Argument requires that God can be known fully.
God is a witness to himself being One, and we witness then through himself, as do God's Angels and those possessing knowledge (Prophets and Imams and holy chosen ladies), and so the way to know him is to make use of his light that emanates from him about himself.
We can't see beyond God's Name which is his greatest title which is his living world of light, but it happens to be sky light reality has infinite pointers traveling and pointing back to the source, and receiving constantly infinite beauties and glories and lights from the source.
Now let me explain how that has to do with us knowing he is necessary aside from just knowing like know God is good, beautiful, great, from making use of God's light and looking the source from a distance.
God's greatest sign and sky has no holes from horizontal side of God's absoluteness, we can see no "holes" and so perfectly manifests infinite attributes. Horizontally, it's proven there is nothing God lacks. The highest sky (7th heaven), also, all infinite attributes that appear descending and differently within the lower heavens and earths, are also somehow at singular funnel point, a center point, this point also points to God, that point shows God is absolute Size as well and is returning to it. Without God as the Absolute Being, there is no direction towards God, no ascending of light, no descending of blessings, thus God's sustenance and in the sky is what we are promised, proves he is the absolute being.
So I'm saying, the ontological argument should not be an end. It should make people want to see God's sky and sustenance and lights of his face, and see him beyond just attributes we give to him (all good, all wise, etc).
There lies the highest signs which bring the highest certainty. God's sustenance is also higher and better, and is the main reward of the next world.