Thanks to Particular Voices for posting a page from William Perkins’ commentary on Galatians 3:12. Thanks to Rich Barcellos for pointing me to it. I took the liberty of transcribing the text and updating the spelling to make it more accessible.
Perkins (1558–1602) was one of the fountainheads of Reformed theology and piety in the English-speaking world. He was one of the major influences on the Westminster Divines and also a major influence on the development of European Reformed theology. The earliest edition of the commentary I found (in a quick search) was the 2nd edition from 1604. There is a modern facsimile edition published in 1989.
This section illustrates that what apparently some still find shocking was commonplace and entirely non-controversial in the classic era of Reformed theology: the Protestant distinction between law and gospel and the notion that the same law given to Adam was “repeat[ed]” after the fall. For Perkins these doctrines were part and parcel of his understanding of justification sola gratia, sola fide and for his understanding of redemptive history. Note too that, for Perkins, these doctrines were entirely compatible to a high doctrine of sanctification and Christian piety. In short, William Perkins, that great Reformed worthy, in order to urge believers to sanctification, did not resort to putting them back under the law for justification.
When Paul says “the Law is not of faith” he sets down the main difference between the Law and the Gospel. The Law promises life to him that performs perfect obedience and that [life] for his his works. The Gospel promises life to him that does nothing in the cause of his salvation but only believes in Christ: and it promises salvation to him that believes, yet not for his faith faith or for any work else but for the merit of Christ. The law then requires doing to salvation and the Gospel believing and nothing else.
We must here further observe that believing and doing are opposed in the article of our justification. In our good conversation they agree: faith goes before and doing follows but in the work of our justification they are as fire and water. Hence I gather that to the justification of a sinner there is required a special and an applying faith for general faith is numbered among the works of the law and the devils have it. This kind of believing therefore and doing are not opposite. Again, here I gather that works of faith and grace are quire excluded from justification because the opposition does not stand between believing and the works of nature but simply between believing and doing.
Lastly, it may be demanded why the Lord says “He that does the things of the law shall live” considering that no man since fall can do the things of the law?
Answer: The Lord since man’s fall repeats the law in his old tenor not to mock men but for other weighty causes. The first is to teach that the law is of a constant and unchangeable nature. The second is to advertise us of our weakness and to show us what we cannot do. The third is to put us in mind that we must still humble ourselves under the hand of God after we have begun by grace to obey the law because even then we come far short in doing the things the law requires at our hands.