The faith that changes the life and connects to God is best conveyed by the word "trust." Imagine you are on a high cliff and you lose your footing and begin to fall. Just beside you as you fall is a branch sticking out of the very edge of the cliff. It is your only hope and it is more than strong enough to support your weight. How can it save you? If your mind is filled with intellectual certainty that the branch can support you, but you don't actually reach out and grab it, you are lost. If your mind is instead filled with doubts and uncertainty that the branch can hold you, but you reach out and grab it anyway, you will be saved. Why? It is not the strength of your faith but the object of your faith that actually saves you. Strong faith in a weak branch is fatally inferior to weak faith in a strong branch.
This means you don't have to wait for all doubts and fears to go away to take hold of Christ. Don't make the mistake of thinking that you have to banish all misgivings in order to meet God. That would turn your faith into one more way to be your own Savior. Working on the quality and purity of your commitment would become a way to merit salvation and put God in your debt. It is not the depth and purtity of your heart but the work of Jesus Christ on our behalf that saves us.
– Tim Keller, The Reason for God