Jacob said he and the other prophets wanted their descendants to know that clear back in the sixth century before Christ, their fathers knew of Christ and had hope in his glory. He said this was also true of the all of prophets from the beginning of time.
Isaiah said the ancient prophets believed in Christ and worshiped the Father in his name. Jacob said the same thing was being done in his day and that was why they kept the law of Moses because it pointed the minds of the people toward Jesus Christ. Jacob said that keeping the law was accounted to them for righteousness just as the faith of Abraham was accounted to him for righteousness. Jacob then said that Abraham's offering of Isaac was merely a similitude of the Father and how he would feel when his only begotten Son would be sacrificed. This is a choice passage, and the only one which clearly states that Abraham's offering of Isaac was a teaching device designed to help Abraham appreciate more deeply what a terrible ordeal our Heavenly Father had to endure at the time of Christ's crucifixion.