Those who trust in the Lord are like Mount Zion, which cannot be shaken but endures forever. As the mountains surround Jerusalem, so the Lord surrounds His people both now and forevermore. (Psalm 125:1,2 NIV)
Mountains? And the Lord like the mountains? What is that? It is fortification, it is strength, it is protection. And what is the point of fortification if there is nothing against which to be fortified? Away back in Old Testament times, when the people came into the land, the remarkable thing is that they occupied the higher places more than the lower. You will find that their towns, cities and villages are almost all of them upon some high place; the reason being that their enemies, who had chariots and horses, had their strength on the level, in the plain, but they could do nothing with chariots and horses against mountains. And therefore the safety, security and fortification of the Lord’s people was by being on high places.
That is a parable. If the enemy can get you on to his level he has beaten you. So he must pull you down, he must get you down, he must get you to accept something less than God’s full place and mind for you, and then he will undo you. That is what he has done with the church, speaking of the church now in very general terms. He has pulled it down to this world level; he has reduced it to the level of things here, and he has absolutely disintegrated it, broken it up and divided it and robbed it of its power. The church which is revealed to us in the New Testament is always on high ground.... In Ephesians, it is “in the heavenlies in Christ Jesus.” It is a great power to be on high ground, it is a great defensive, protective factor; the enemy can do little with you if you keep up there and refuse to come down. Nehemiah found that to be so, when they said, “Come down and let us confer”; and he said, “I am doing a great work so that I cannot come down” (Neh. 6:3). It is a principle operating.
By T. Austin-Sparks from: The Mountains Around Jerusalem - Chapter 1