“… false brethren unawares brought in, who came in privily to spy out our liberty…”

And that because of false brethren unawares brought in, who came in privily to spy out our liberty which we have in Christ Jesus, that they might bring us into bondage: ~Galatians 2:4 KJV

Wrong Interpretation:

Christians who think they will never be perfect— and are inclined to see grace as an excuse for that mentality— use this liberty scripture to blame “religious” Christians or strict doctrine followers.

Right Interpretation:

The apostle Paul is again referencing circumcision. The false brethren who were coming into the church believed that the old covenant of circumcision created by hand was still important. Therefore, they were spying out the Christian liberty of being under Christ’s circumcision, which meant that a man did not need to be physically circumcised anymore to be clean; only have faith and believe in the New Testament doctrine of Christ, which is the circumcision of the heart.

This is the previous scripture,

But neither Titus, who was with me, being a Greek, was compelled to be circumcised: ~Galatians 2:3 KJV