Now faith is the assurance of things hoped for, the conviction of things not seen. Indeed, by faith our ancestors received approval. By faith we understand that the worlds were prepared by the word of God, so that what is seen was made from things that are not visible.
Hebrews 11:1-3 (NRSV)
Or, again:Faith is the capacity to put all your eggs in the one basket, when even the existence of the basket must be taken on trust and hope. It was the ability to take decisive action based on faith alone that made our forebears such memorable heroes. Even our belief that the universe came into existence on God’s say-so is based solely on faith. The existence of material things might be provable, but the belief that their origins lie in something that is not accessible to scientific observation can only be grounded in faith.
Hebrews 11:1-3 (Laughing Bird Paraphrase)