At the third new moon after the Israelites had gone out of the land of Egypt, on that very day, they came into the wilderness of Sinai. They had journeyed from Rephidim, entered the wilderness of Sinai, and camped in the wilderness; Israel camped there in front of the mountain. Then Moses went up to God; the Lord called to him from the mountain...Jesus "went out to the mountain to pray; and... spent the night in prayer to God." (Luke 6.12) In fact he made a habit of it: "many crowds would gather to hear him and to be cured of their diseases. But he would withdraw to deserted places and pray." (Luke 5.15b-16)
George Fox climbed Pendle Hill,
As we went I spied a great high hill called Pendle Hill, and I went on the top of it with much ado, it was so steep; but I was moved of the Lord to go atop of it; and when I came atop of it I saw Lancashire sea; and there atop of the hill I was moved to sound the day of the Lord; and the Lord let me see atop of the hill in what places he had a great people to be gathered.
(from Fox's journal, quoted in Quaker faith & practice)Part of it may simply be that climbing a hill is an act, not of some naive attempt to get physically closer to a God conceived of as "up there", but of deliberately putting ourselves in the way of hearing from God. It may be the same impulse that leads us to silence and stillness in the awareness of God's presence. A prayer like the Jesus Prayer, the "prayer word" in Centering Prayer, or the word "maranatha" in Christian Meditation, at least in part, seeks to do the same thing, to lead us to a state of inward withdrawal from the world of getting and doing into a condition of inner receptiveness, as Jesus explained:
But whenever you pray, go into your room and shut the door and pray to your Father who is in secret; and your Father who sees in secret will reward you.
(Matthew 6.6)(For what reward could God give us better than the gift of God's presence?)
William Penn summed it up,
And you, young convinced ones, be you entreated and exhorted to a diligent and chaste waiting upon God, in the way of his blessed manifestation and appearance of himself to you. Look not out, but within… Remember it is a still voice that speaks to us in this day, and that it is not to be heard in the noises and hurries of the mind; but it is distinctly understood in a retired frame. Jesus loved and chose solitudes, often going to mountains, to gardens, and sea-sides to avoid crowds and hurries; to show his disciples it was good to be solitary, and sit loose to the world.