You will keep in perfect peace him whose mind is steadfast, because he trusts in You.
Trust in the LORD for ever, For the LORD, the LORD, is the Rock eternal.
On their first missionary journey, Paul and Barnabas planted churches in Antioch, Iconium, Lystra and Derbe. In each of these places, they were forced to move on after just a few weeks because of persecution. How could all these new Christians be expected to maintain their faith under such circumstances? Paul and Barnabas knew the answer (Acts 14:23). Christians are secure in their faith not because of any power in themselves, but because of where their trust is placed: in the God who is eternal and whose promises therefore will not fail (Titus 1:1,2).
In a rapidly changing world, God is the one unchanging reality. In the Old Testament (and especially in the Psalms) He is often compared to a rock: a place of shelter from wind and from burning sun, and a place of safety when under attack (e.g. Psalm 31:1-3). This was a truth that the Israelites learned early in their history (although they often forgot it!) when wandering in the desert; they were forced to depend on God, and they proved in their own experience that He would not let them down (Deuteronomy 32:4).