The fact that we can so easily become distracted at prayer is proof of just how inadequate our ideas of God and the Heavenly Court really are. For, of course, if we had even a faint understanding of just what we were dealing with, it would be almost impossible for anything else to have a hold on our mind. This, so I would imagine, is the cause of the phenomenon of ecstasy that some Saints have experienced, wherein they become utterly insensible to their surroundings in their contemplation of the divine.
Yet, of course, this mental veil is itself a mercy, since in this world we have to be able to think of other things. This is one way in which it’s true to say that no mortal can see the Face of God and live (remember what happened to Semele in the Greek myth). It won’t be until we are made new in eternity that it’ll be safe for us to actually see God as He is.