Luke has these additional words of Christ in verses 31-32, not quoted by the other Gospel writers. They are marvellous because at first they almost overlook the blame that attaches to Peter in what is going to take place, and go straight to the comfort and strengthening he will need to recover from this fall.
What is this faith system? It is this: that all our troubles and concerns and our needs and our problems as the Lord's people, we take to him in prayer, we do not try to do everything in our own strength. God does not take over the battle of living the Christian life from us. He has given us the faculty of faith, and we are to use it, but we are to use it in prayer to God, that he will strengthen us and bless us. Every problem we get, every duty we are set by the Lord, we are to make a matter of earnest prayer and dependence upon him. As we do so he will hear those prayers, and he will answer us, and we will have the tremendous experience of knowing these supernatural sustaining blessings. The life of faith is a life which daily says, ‘I'm going to prove the promises of the Lord; I'm going to commit all my way to him; I'm not going to walk about – as we all do day after day, week after week – worried sick about this, worried sick about that. I'm going to learn to commit these things to the Lord. I'm not going to abdicate mental responsibility for weighing up things and considering things, but I am going to commit them to the Lord and prove his power and his blessing.’ That's the faith system in the life of a Christian.
Answered prayer is a great source of assurance. We walk about for two or three weeks, worried and depressed about a thing – which we shouldn’t be – but as soon as we apply it to prayer and to the Lord, he clears our mind. He blesses us in his time; he helps us and we know he is doing so. It may take a week, two weeks, three weeks, three months, three years, but we trust that in his good time on every issue in life he will make us more than conquerors as we have the answers to our prayers. We have all the blessing of these things happening, things that we could not have done for ourselves, working out and turning out for good. But when faith breaks down, when the constant application to prayer and looking to God breaks down, then the devil can sift us like wheat; we are in his hands. If that system has consciously broken down in the life of a Christian over recent weeks, you must humble yourself and reapply to God for help.