In virtue of faith, things hoped for, are now. So faith is their essence, or substance, in regard to the actual experience of the believer. By faith the future and the unseen can be made real for men. The spiritual history of man is taken as proof of the power faith has to try and realize the unseen. By realizing the future and apprehending the unseen, in the atmosphere of faith, the inspired lives of the elders bore witness to their faith.
Faith is a clear understanding of the revealed Word of God.
Abel knew life must be given for life. Eve's relationship with the Serpent, brought death in the bastard, Cain, for whom there was no atonement. By revelation Abel knew he was a son of God, and offered the substitutionary life of an innocent lamb, speaking of the coming Messiah Who, through the virgin birth would not have original sin imputed. Thus His sacrifice, without spot or blemish, was acceptable to God. Abel's sacrifice was the evidence of his righteousness - the true connection to God was faith to which God bore witness by receiving his faith.