Thin places are where the veil between heaven and earth is so thin that the two realms effectively operate together as one, which has always been God’s intention from the beginning. It takes both the realm of heaven and the realm of earth to make a world. Tops of mountains are therefore the real estate of choice of cultures down through history for building temples, for in the high places of the world heaven and earth kiss. Temples are engines for making a world. The dwelling of the Greek gods on Mt Olympus, for example, is a cultural way the Greeks developed the idea of thin places in their creation of the Greek world. The Greeks, like all cultures, whether they realize it or not, are compelled to form thin places because this impulse is rooted in the reality God authored when He originally established Eden on a mountain and then later had Solomon build the Temple on Mount Zion. The impulse is planted deep in the nature of man who is created in God’s image as a co-creator in the making of the world. Poetically speaking, Christ and His Body the Church are together the archetypal thin place where heaven opens up to the earth and angels ascend and descend (Jn. 1:51). This dynamic of ascending and descending is one of the most fundamental aspects of the entire adventure of salvation, which can be summarized this way: Christ became like us (in His descent from heaven, which we celebrate at Christmas), that we might become like Him (in His ascent from Hades, which we celebrate at Pascha or Easter). Thus Christmas and Pascha point to the two-way traffic that flows back and forth at a thin place. Because Jesus described Himself as a thin place person (Jn. 1:51), all who are in Christ are called to be thin place people who cultivate thin places in everyone and everywhere in order to establish the world as the dwelling place of God with mankind.
Also see Celtic Community Builders, and Theosis.