Here is an excerpt from Pope Benedict on the Theology of kneeling, with a link to the full article below.
The Christian Liturgy is a cosmic Liturgy precisely because it bends the knee before the crucified and exalted Lord. Here is the center of authentic culture – the culture of truth. The humble gesture by which we fall at the feet of the Lord inserts us into the true path of life of the cosmos.
There is much more that we might add. For example, there is the touching story told by Eusebius in his history of the Church as a tradition going back to Hegesippus in the second century. Apparently, Saint James, the “brother of the Lord”, the first bishop of Jerusalem and “head” of the Jewish Christian Church, had a kind of callous on his knees, because he was always on his knees worshipping God and begging forgiveness for his people (2, 23, 6). Again, there is a story that comes from the sayings of the Desert Fathers, according to which the devil was compelled by God to show himself to a certain Abba Apollo. He looked black and ugly, with frighteningly thin limbs, but most strikingly, he had no knees. The inability to kneel is seen as the very essence of the diabolical.
But I do not want to go into more detail. I should like to make just one more remark. The expression used by Saint Luke to describe the kneeling of Christians (theis ta gonata) is unknown in classical Greek. We are dealing here with a specifically Christian word. With that remark, our reflections turn full circle to where they began. It may well be that kneeling is alien to modern culture — insofar as it is a culture, for this culture has turned away from the faith and no longer knows the one before whom kneeling is the right, indeed the intrinsically necessary gesture. The man who learns to believe learns also to kneel, and a faith or a liturgy no longer familiar with kneeling would be sick at the core. Where it has been lost, kneeling must be rediscovered, so that, in our prayer, we remain in fellowship with the apostles and martyrs, in fellowship with the whole cosmos, indeed in union with Jesus Christ Himself.