13 For the promise, that he should be the heir of the world, was not to Abraham, or to his seed, through the law, but through the righteousness of faith. (Romans 4:13 KJV)
William Burkitt’s Commentary
That is, the great promise which God made to Abraham and his seed that they should possess that rich and pleasant part of the world, the land of Canaan, under which also heaven itself was typically promised and comprehended, was not made upon condition of their performing perfect obedience to the law, but they were to obtain it by faith; that is, by trusting to, and depending upon the gracious promise of a faithful God.
Note here, The argument couched for justification by faith without works, which is the apostle’s grand scope, design, and drift; it runs thus: “If a promise made to the father of the faithful was accomplished, not by legal obedience, but by the righteousness of faith; then it follows, that all his children are justified by faith as Abraham their father was. But the promise of the earthly inheritance, and under it, of the heavenly one, was accomplished not by the law but by the righteousness of Abraham’s faith: Therefore, justification is not to be expected by the works of the law, but by faith alone.”