Between the dimension of absolute transcendence of religious holiness and that of relative immanence of earthly worldliness, there is some tension of fracture and interaction. This is especially true of the dialectical tension between the mystics of holy transcending above earthliness and the openness of the holy calling to the world. A system of religion itself is actually the medium and mediation in - between holiness and earthliness, absoluteness and relativity, Infinity and finitude, spirituality and materiality, eternity and contemporariness and so on. And the mystics, which incarnate the most profound religious experience, present also the peak of mutual opening between divinity and humanity. This essay will take Christianity as paradigm and its origin of its German theology and philosophy in the German culture as an example, to illustrate the dialectical relationship between the mystics and openness. This essay will outline the implicated dialectics between mystics and openness in the systemic theology of Christianity, which is itself a triune systemics of theological dogma, sacred text and community of belief. Hereafter it will explore preliminarily this dialectics in Meister Eckhart's mystic thinking as the genesis of German Christian theology and philosophy, in particular of German Mysticism. Finally it will reveal the main clue of the development of German theology and philosophy in the German movement of spirit (Geist).