Listen! I, Paul, tell you that if you let yourselves be circumcised, Christ will be of no benefit to you at all!
And I testify again to every man who lets himself be circumcised that he is obligated to obey the whole law.
(NET)
Having begun to turn toward expounding the wonderful liberty found in a life lived by faith in Jesus, Paul here gives an example of the opposite, of the yoke of slavery mentioned in v.1.
Using circumcision as the particular example of the wider problem, Paul says look, if you let yourselves be circumcised, the grace of Jesus, being justified by faith alone, and the wonderful liberty in life that comes with that will be of no benefit to you at all. Paul is not against circumcision totally (cf. Acts 16.1-3), but is most certainly against using this as a ‘work’ to be added to faith in the seeking of salvation. As Donald K. Campbell writes,
Anyone who was circumcised for that reason added works to faith and demonstrated that he had not exercised saving faith in Christ.
Then, Paul adds what should be a hammer-blow to this idea of supplementing faith with a little law. He writes to the Galatians that every man who lets himself be circumcised…is obligated to obey the whole law. It’s a complete unit, the law, and if we break a little of it then in essence we’ve broken all of it (James 2.10). To use an example we’ve talked about before, being caught speeding is breaking the traffic law of the land. Running a red light is breaking the traffic law of the land. Contravening one individual commandment of the law is, in principle, breaking the whole law and brings with it the associated consequences.
We can see Paul’s line of thinking and we can ask ourselves what he is asking the Galatians: why on earth would we trade the life of liberty that comes to us via faith in Jesus for a life of law, legally-lensed thinking, consequences, curses, and debt? Put like that, I don’t think anybody would consciously want to. But, sadly, that was happening in the lives of the Galatians. They were being told and taught that to be a real believer, to be a real Christian (so to speak), to really be good with God, you need to do this and that in addition to believing in the Messiah.
This is such a slippery slope and one I hope that you are on constant guard against falling down. Many well-intentioned Bible teachers will say that you need to do this or that, that a certain passage teaches that you need to add this or that to your character and conduct, and that this is really what a Christian life is like. Do you see the similarities there? Good intentions, perhaps. Adding burdens to weary people, for sure.
God’s Word to us certainly does contain things for us to add to our character, elements of our conduct that we could improve, change, or simply lose. But, at the core, I truly believe that it is one big testimony to the truth of Jesus, and so did He (John 5.39, Luke 24.27, for example).
All of this to say, for you and for me there is a real need to stand firm in what we know is true about the life of a Christian, one who has put faith in Jesus for their justification and for the forgiveness of their sins. When we are told to add anything to this, that we need to do something to activate this, or that, you know, now you believe this, here is a list of do’s and don’ts, we need to remember the words of Paul to the Galatians in 5.1-3 and remember that Jesus’ death and resurrection are all you need to be justified before God.