Why were all nations going to be blessed through Abraham?
All nations would be blessed through Abraham because the promised Christ came through Abraham's line. Though the covenant people rejected and crucified Him, He became Savior of the whole human race, not Israel alone. God would justify the heathen, or non-Jew, by faith, as the gospel was preached beforehand to Abraham.
Les explains that this promise goes back to Genesis 12:3. It would be through the covenant promises with Abraham that the whole human race would enter into a salvation experience. Why? Because through the promise of Abraham came the Christ. Even though the covenant people rejected Him and nailed Him by the Roman army to a cross, He became the Savior, not of Israel alone, but of the whole human race. Abraham himself entered in by faith and faith alone based on what God said to him, which was simply, Leave Ur. He was a believer and was declared righteous before he got out of town because he believed God. Les applies this same pattern to us: genuine salvation is followed by a changed life and lifestyle.