Trust is a difficult thing to give. For my part, I give it sparingly. I do not trust many folks and I am reluctant to trust again if a trust is broken. I do not think this makes me terribly unique, it just makes me a standard issue person.
Isaiah gives the instruction to trust in the LORD forever. This is challenging for those of us who do not trust easily. We may want to trust God, but find it difficult to do. Trust is not a normal practice for us. Our trust muscles are underdeveloped. Add to this the fact that our fellow people will often betray our trust and make it more difficult to trust the next person to come along. God gets mixed up in all of this. And our ability to trust Him is impaired by the actions of people.
But Isaiah does not simply instruct me to trust God, he also gives me a reason to do so. He reminds me that God is an everlasting Rock. For anyone who has gone swimming in the ocean, you know the value of a rock. The waves pummel you and the current pulls at you, but that rock is singularly unimpressed. It cannot be impressed. It is a rock. If I cling to the rock, the waves and current will impact me and pull at me, but I can be steadfast so long as I cling to and depend on the rock. The moment I trust my own ability to swim or my own strength to fight the current, I will be subject to all the whims of the waves. And oceans are capricious.
Translate all that over onto God being an everlasting Rock. The imagery is meant to communicate permanence and immutability; stability and safety. In short, the imagery communicates something of the nature of God. He is immutable (perfection has no need to change) and stable and a safe haven for those who would shelter in Him. All of the things about people that make it difficult to trust them are negated by this description of God. People change, but God does not. People come and go, but God abides forever. People are wibbly wobbly creatures, but God stands firm. People are dangerous to trust in and prone to betrayal, but God is a safe haven.
Am I trusting God today? If yes, I should carry on and be encouraged. If no, I need to do so.