How did the Pauline expression "The Works of the Law" come to be equated with acts of righteousness, good works and keeping God's commandment?

I have been taught all my Christian life that the uniquely Pauline expression "the works of the law" found in the Epistle to the Romans and the Epistle to the Galatians refers to acts of righteousness, good works and keeping God's commandment. So when Paul denounces the works of the law as lacking justification value, it is taught that it is acts of righteousness, good works and obedience to God's commandments that he denounces. Even though I often wrestled with this identification when I read some passages of Scripture that seem to contradict it, I generally accepted it as the truth. I have however studied the expression and the context in which it is used by Paul and have found it to be referring to circumcision and contingent works and not to righteousness, good works or acts of obedience to God's moral law. I am now curious to find out the origin of the interpretation. I want to be sure I have not missed anything that was considered to arrive at it which makes my conclusion to differ. Has anyone done a study on this or come across any exposition giving the background to this interpretation?