Once upon a time, there was no difference between theology and mysticism, just like there was no difference between philosophy and science. Science (“natural philosophy”) was an integral part of the quest for wisdom, just as mysticism (“ascetical theology”) was an integral part of the quest for wisdom of God.
Ken Wilber talks about how it was a good thing for humankind to reach the point where we were able to differentiate between “external” forms of wisdom (physics, chemistry, biology, etc.) and “internal” forms of wisdom (theology, mysticism, morals, etc.). The current mess we’re in (where religious thinking has been exiled from the scientific community, where fundamentalist Christians insist that the theory of evolution is “anti-God,” and where advances in technology are embraced often with little or no public debate about their moral or spiritual value), however, stems not from this necessary differentiation of different fields of human wisdom, but rather from their dissociation, as religion and science have basically been warring against one another in the west for at least the last three hundred years (a battle that, thanks to folks like Richard Dawkins and Christopher Hitchens, we can see is still alive and well).
Perhaps mysticism and theology have suffered a similar fate. While their differentiation (a process that may have began as early as 500 CE with the writings of Pseudo-Dionysius, and was pretty much in place by the time John of the Cross rolled around a millennium later) was probably an important part of the unfolding of Christian wisdom, the subsequent dissociation of mysticism and theology (where theology has increasingly become abstract and arcane on the academic level, and concerned only with moral behavior on the popular level; meanwhile mysticism has retreated either into conservative devotionalism or liberal relativism, both marred by an appeal to emotional experience which subtly masks an anti-intellectual, anti-rational foundation) is, as in the case of the dissociation between science and religion, a disaster.
At its best, theology is like classical or Newtonian physics while mysticism is like modern or quantum physics. Neither one repudiates the other; they simply represent different fields of inquiry that hopefully complement one another and indeed can illuminate one another. We need mysticism grounded in theology, and theology grounded in mysticism. And this isn’t going to emerge from the pulpits or the universities. If the Holy Spirit wants to lead us into a re-integration of theology and mysticism, I suspect that such a re-integration will begin in the hearts and minds of ordinary people who are taking time to pray, to meditate, to contemplate, and to reflect on who they are and what their Christian vocation might be. We are all parts of the body of Christ, not just those of us who get paid to be. So let’s all start praying about how we can get the Body’s heart and head back in harmony with each other.