We're told that Abraham believed God. That is faith.
It is the Gospel of Christ, but shrouded in type and shadow. The curtains weren't parted for him, but he believed God.
I think you underestimate the revelation provided by God to Abraham. I think much of the underestimation is due to the apostate condition of Israel at the time of Christ. Apostate Israel at the time of Christ knew less about the gospel than what was known prior to the interBiblical period. Abel knew more about the gospel than apostate Israel at the time of Christ and Isaiah knew even more (Isa. 53). Sure they did not understand the timing or the details concerning his future ministry (1 Pet.1) but they understood the essence of the gospel that God had promised to provide a Savior from their sins - Acts 10:43.