Genesis 15:6 is clear: After hearing the promise of God, Abraham “believed the Lord, and he counted it to him as righteousness.” The Apostle Paul quotes Genesis 15:6 and uses Abraham as an example of justification by grace through faith: “For if Abraham was justified by works, he has something to boast about, but not before God. For what does the Scripture say? ‘Abraham believed God, and it was counted to him as righteousness’” (Rom. 4:2-3).

Genesis 11:31‑12:3 records how God called Abraham out of Ur of the Chaldeans. This call was 8‑10 years before the time when “Abraham believed God, and it was counted to him as righteousness” (Gen. 15:6; Rom. 4:3). In this light, look at the striking comments John Calvin makes on Genesis 15:6.

We must now notice the circumstances of time. Abram was justified by faith many years after he had been called by God; after he had left his country [in] a voluntary exile, rendering himself a remarkable ...