How did Abraham understand the promise made to him? After having heard the gospel, Abraham saw the ultimate fulfillment of the promises made to him in Christ. He realized that they were not earthly, carnal promises, but heavenly promises for a heavenly country. The Hebrews writer tells us that after a generation of wilderness wondering (Hebrews 3-4), the Israel of God had arrived at the Heavenly Jerusalem. This is associated with the passing away of the Old Covenant and the full reception of the kingdom not made with hands. Hebrews and Jesus taught the same thing (Matthew 5:3ff).
Abraham Had Two Sons: http://labornotinvain.com/podcastarchives/abraham-had-two-sons/