What is the Reformed Interpretation of Galatians 5:4?

The Reformed Protestant interpretation of Galatians 5:4 is simple and straightforward, and I will provide extracts from two Reformed ministers. However, what confuses me is your attempt to link this to the Calvinistic doctrine of ‘Perseverance of the Saints’. You do realise there is more than one Calvinistic school of thought – hyper-Calvinism being the extreme version.

Here is a partial quote from Matthew Henry (1662-1714) a Reformed Protestant minister who is best known for the six-volume biblical commentary ‘Exposition of the Old and New Testaments.’ This is his summary of Galatians 5:1-12 which gives an overview:

Verses 1-12: In the former part of this chapter the apostle cautions the Galatians to take heed of the judaizing teachers, who endeavoured to bring them back under the bondage of the law. He had been arguing against them before, and had largely shown how contrary the principles and spirit of those teachers were to the spirit of the gospel; and now this is as it were the general inference or application of all that discourse. Since it appeared by what had been said that we can be justified only by faith in Jesus Christ, and not by the righteousness of the law, and that the law of Moses was no longer in force, nor Christians under any obligation to submit to it, therefore he would have them to stand fast in the liberty wherewith Christ hath made us free, and not to be again entangled with the yoke of bondage.

In the first section he goes on to explain how some of the Christians in Galatia were being led astray by Judaizers:

We are not to suppose that it is mere circumcision which the apostle is here speaking of, or that it was his design to say that none who are circumcised could have any benefit by Christ; for all the Old-Testament saints had been circumcised, and he himself had consented to the circumcising of Timothy. But he is to be understood as speaking of circumcision in the sense in which the judaizing teachers imposed it, who taught that except they were circumcised, and kept the law of Moses, they could not be saved, Acts 15:1.

That this is his meaning appears from v. 4, where he expresses the same thing by their being justified by the law, or seeking justification by the works of it. Now in this case, if they submitted to circumcision in this sense, he declares that Christ would profit them nothing, that they were debtors to do the whole law, that Christ had become of no effect to them, and that they were fallen from grace. From all these expressions it appears that thereby they renounced that way of justification which God had established; yea, that they laid themselves under an impossibility of being justified in his sight, for they became debtors to do the whole law, which required such an obedience as they were not capable of performing, and denounced a curse against those who failed in it, and therefore condemned, but could not justify them; and, consequently, that having thus revolted from Christ, and built their hopes upon the law, Christ would profit them nothing, nor be of any effect to them...

Thus, as by being circumcised they renounced their Christianity, so they cut themselves off from all advantage by Christ; and therefore there was the greatest reason why they should stedfastly adhere to that doctrine which they had embraced, and not suffer themselves to be brought under this yoke of bondage. Note, (1.) Though Jesus Christ is able to save to the uttermost, yet there are multitudes whom he will profit nothing. (2.) All those who seek to be justified by the law do thereby render Christ of no effect to them. By building their hopes on the works of the law, they forfeit all their hopes from him; for he will not be the Saviour of any who will not own and rely upon him as their only Saviour.

In section 2 the implication is that if they expected to be justified and saved in any other way they were likely to meet with a disappointment, and therefore Paul was greatly concerned to encourage them to adhere to the doctrine of the gospel which they had embraced. Source: https://www.christianity.com/bible/commentary/matthew-henry-complete/galatians/5

Another reformed protestant stalwart, Charles H. Spurgeon, delivered a sermon in London on 6 September 1866 on the topic of circumcision, based on Galatians 5:6: “For in Jesus Christ neither circumcision availeth anything, nor uncircumcision, but faith which worketh by love.” After exposing the false teachings on circumcision (adhering to the law) he goes on to say this in section 1, THE OUTWARD PART OF RELIGION:

Of course, it [circumcision] was in Paul’s day the outward mark of the firm believer in Judaism. The man who still held to the old faith was not to be led away by the innovations, as he supposed them to be, of Jesus of Nazareth, but still held that it was essential, first and foremost, that the seed of Israel should bear in the flesh the ordained mark...

Paul sweeps away the whole of the Jewish ceremony, both in its observance and in its non-observance, and so he gives it a twofold blow and lays it dead... The true essence of the thing lies in the faith which works by love, and if you have received it without faith, you have received nothing at all. You have received only the mere outward ceremony and there has no good come to your soul. Source: https://www.spurgeongems.org/sermon/chs3454.pdf

The doctrine of the Judaizers was a mixture of grace (through Christ) and works (through the keeping of the Law). This false doctrine was dealt with in Acts 15 and strongly condemned in the book of Galatians.

At the Jerusalem Council in Acts 15, a group of Judaizers opposed Paul and Barnabas. Some men who belonged to the party of the Pharisees insisted that Gentiles could not be saved unless they were first circumcised and obeyed the Law of Moses. Paul made the case that, in Christ, there was no longer any distinction between Jew and Gentile, for God had purified the hearts of the Gentiles by faith (Acts 15:8–9). He said it plainly in Galatians 2:16: “A man is not justified by observing the law, but by faith in Jesus Christ. So we, too, have put our faith in Christ Jesus that we may be justified by faith in Christ and not by observing the law, because by observing the law no one will be justified.”

To add anything to the work that Christ did for salvation is to negate God’s grace. We are saved by grace alone, through faith alone, not by returning to the Law. “I do not set aside the grace of God, for if righteousness could be gained through the law, Christ died for nothing” (Galatians 2:21). Source: https://www.gotquestions.org/Judaizers.html

Were the Judaizers saved by grace? Had they been adopted into God’s family and were they counted amongst the saints? From Paul’s condemnation of them it would seem they had not yet come to saving faith in Christ alone and that they were still clinging to the Law. Not sure there is any point in trying to link this to Calvinism and the ‘Perseverance of the Saints’.