Faith is not ethereal. It is not a wishing on a star and believing that positive thoughts overriding negative feelings will make wishes come true. It is a belief based on the reliability of past experiences.
When you sit in a chair, you believe, based on past experience that the chair will support your weight. You accept, on faith, without getting down on your hands and knees to verify, that it is safe to sit in the chair. You have, at some point in your life, seen a chair not hold a person sitting in it, but based on probabilities of the dependability of the chairs in your life, your faith in that chair is confident. The under girding of that belief is based on the fact that you sit in chairs all the time and rarely, or perhaps never, are you tossed out on your backside. The evidence not seen is that despite the fact that you have not examined the chairs reliability, you feel there is enough evidence by chairs of the past to verify it will hold you provided you observe the laws that will prevent you from being tossed out. You have FAITH in that chair. You're not sitting in thin air, hoping that a chair materializes; you're sitting on a chair that you believe will support your weight.
Now, put that established chair on a place where falling out of it will result in certain death, and the level of faith is probably going to be drastically reduced. Whereas you would have sat down on the chair without a second thought on your kitchen floor, if that chair is balanced on 2 beams stretched out over the Grand Canyon, your faith in it will waiver or perhaps break down, entirely. Over a course of time, given the opportunity to establish that the beams are secure and that the chair will not act any differently on the beams than on your kitchen floor, you may build the faith to be able to sit in that chair.
That's what Faith is. It is a belief contingent on past performance creating a hope of future conduct. It is established in the testing and trying of the reality of God's word. If a person is not willing to test God's word, by putting himself under the authority of His Law, and abide under the conditions of God's Word, then one may not establish a claim that there is no proof of the reality of God's word, anymore than one can say a chair is not reliable to sit in based on the fact that they are not willing to sit in it or that they fell out of it, trying to stand on their head.
Many professed Christians give irrational explanations of what faith is because they are unwilling to put themselves under the authority of God's word or law or risk relying on what they, quite frankly, do not know. One establishes that faith by incorporating the word of God into their lives according to the way established by God. In other words, you begin to obey it. You begin keeping the laws of God, to try to follow His words as He has laid them out, even in the face of adversity and you then begin to see that God is taking care of you. Things begin to work out so that you can obey. The further you test it, the more it establishes your faith' because you run into impossible situations that work out in the most incredible ways. And so you start to incorporate more of God's word into your life.
You establish the reliability of the Word of the God of the Bible exactly the same way you establish that a chair is safe to sit in'perhaps even to the point of being comfortable even if the chair is perched on a precipice. Even though you see others around you fall out of other chairs (like drunks or babies who cannot sit up or like children using the chair incorrectly) or you've seen it collapse (under too much weight or abuse or neglect), you learn the rules, or follow the Word and you see that the chair is reliable, if the sitter is faithful to the conditions of the chair.
One learns the reliability of the Bible through use, making clear that there is a difference in "the way that seems right to a man,' over they way that is righteous according to God. You learn to walk by faith in the way that God has established over the way of sight because you come to realize that it is God that establishes reality and what you see with your eyes is not as reliable as the way God has established, because reality is established by God.
And to the degree you have confidence in that way, it defines the level of your faith. Do you have faith in a chair on a solid floor? You have a little faith. Do you have faith in a chair positioned on a sheer drop? You either have great faith or you lack faith. It is confidence in previously established behaviors and assurances over time that build your little faith into great faith.
Abraham had great faith because God gave him a child when his wife was too old to have one and promised him that child would grow into a great nation. He had the child, every day of his life, right there in front of him, as the under girding of his faith-for the very existence of the child was an impossibility. He had a further promise from God that in Isaac, He would establish the seed of Abraham, and the faith of the past of Isaac's impossible birth, gave way to the establishment that God would not allow his word to "come back to him void' giving Abraham the confidence to believe.
This is how faith grows: the past experience, the establishment that God's word is wholly reliable, leads you to be able to go forward in the face of uncertainty or even in the face of certain ruin, knowing God holds reality in the palm of his hand.
Simply put, faith is trusting God with what is in front of you because of what He has done behind you.