From The Cloud of Unknowing:

Christ ascended physically in the presence of all his disciples and sent the Holy Spirit as he had promised; and you feel that all this proves that you should literally direct your mind upward during prayer. We do indeed believe that Christ in his risen humanity ascended to his Father, but let me try to explain again why this should not be misconstrued in a literal sense. I will speak as plainly as I can, though my explanation may not yet be adequate.Yes, Christ did ascend upward and from on high sent the Holy Spirit. But he rose upward because this was more appropriate than to descend or to move to left or right. Beyond the superior symbolic value of rising upward, however, the direction of his movement is quite incidental to the spiritual reality.For, in the realm of the spirit, heaven is as near up as it is down, behind as before, to left or to right. The access to heaven is through desire. He who longs to be there is really there in spirit. The path to heaven is measured by desire and not by miles. For this reason Saint Paul says in one of his epistles, "Although our bodies are presently on earth, our life is in heaven."Love and desire constitute the life of the spirit. And the spirit abides where its love abides, as surely as it abides in the body which it fills with life. We need not strain our spirit in all directions to reach heaven, for we dwell there already by love and desire.