The Divine Spirit's presence in the experience of contemplation contradicts the idea we often find in medieval mysticism that contemplation must be reached by degrees, as in the movement from meditation to contemplation, and that it itself may be a bridge to mystical union. The gradualistic thinking belongs to the ambiguities of religion because it faces God as a besieged fortress to be surrendered to those who climb its walls. According to the protestant principle, God's surrender is the beginning; it is an act of his freedom by which he overcomes the estrangement between Himself and man in the one, unconditional, and complete act of forgiving grace. All the degrees of appropriation of grace are secondary, as growth is secondary to birth. Contemplation in the Protestant realm is not a degree but a quality, that is, a quality of a prayer which is aware that the prayer is directed to Him who creates the right prayer in us.Before this startling comment, Tillich has defined contemplation as "participation in that which transcends the subject-object scheme and therefore language itself", and criticized the lack of it in protestant churches. But it is still a very bold thing for a protestant theologian to enter the arena of catholic mysticism with this criticism that seems to come from within that arena rather than from without. The usual protestant criticism of catholic (or any) mysticism is that it is about the individual trying to reach God without relying on God's grace. Here Tillich is much more subtle, and shows greater understanding. He acknowledges that the goal of the mystic is sound, but he questions one of the key metaphors for the process of reaching this goal. Even though this may sound like polemics it is not, it is spiritual guidance. The first step is to become aware of the fact that the walls, so to speak is already torn down, because God has surrendered. The wall does not exist between Me and God, it is a wall within myself. To be aware of this in one's prayer is contemplation.
Systematic Theology III, 192-193.
I would love to discuss the question why military language was so prevalent among the medieval mystics with Tillich. He doesn't give any thoughts on this, at least not here. This would probably be a fruitful starting point for an inquiry into the vision of the world and society in the middle ages.