Faith in God may be simply trust in His goodness. You may have experienced His presence, His life-changing power within your soul. But day-to-day tests and challenges require you to demonstrate trust in Him under new circumstances.
Faith in God may not mean that you don't know for sure that He exists. Rather, it may be the challenge to exhibit trust, as a child who will jump from a tree branch when his daddy says, "Jump, I will catch you." Except that in the adult's walk of faith, he doesn't have the advantage that the child does of hearing an audible voice.
Well said.
It occurred to me last night that the Bible takes the existence of the God of Israel as a given. "In the beginning God created...". Genesis presents no arguments for God's existence. Likewise the faith in the Gospels is faith that Jesus is the Messiah and the Son of God and that He can and will save us from our sins. Once again God's existence is a given.
It is true that there are a few passages that touch on evidence for God's existence, but the vast majority of the Bible treats His existence as obvious.