Treasury of Scripture Knowledge
Now we [all] know that everything the law says applies to those who are under [obligation to obey] that law, [Note: Here "the law" appears to refer to the Old Testament Scriptures generally, since Psalms and Isaiah are quoted. See verses 10-18]. This is so that the mouth of every objector may be stopped [i.e., from making excuses for his sin], and thereby bring the entire world under God's judgment [i.e., both Jews and Gentiles].
For if [only] those who are obedient to the law deserve an inheritance, [then their] faith [in God] is for nothing, and God's promise is nullified.
For Moses wrote [Lev. 18:5] about a person being made right with God by obeying the requirements of the law of Moses, that he would gain [never ending] life for doing this.
Now the law of Moses is not based on one's faith, for [Lev. 18:5 says], "The person who obeys the requirements of the law of Moses will obtain life by doing so."