Galatians 2 - What "liberty" was Paul speaking of? 2020

Gal 2:4
But it was because of the false brethren who had sneaked in to spy out our liberty which we have in Christ Jesus, in order to bring us into bondage.

These false brethren were not good men. They were intentionally attempting to pollute the message of becoming a part of the Kingdom through Yeshua. They were teaching that one must become a Jewish convert and be circumcised in order to be saved.

Acts 15:1-4 And some men came down from Judea and began teaching the brethren, “Unless you are circumcised according to the custom of Moses, you cannot be saved.” 2And when Paul and Barnabas had great dissension and debate with them, the brethren determined that Paul and Barnabas and certain others of them should go up to Jerusalem to the apostles and elders concerning this issue. 3Therefore, being sent on their way by the church, they were passing through both Phoenicia and Samaria, describing in detail the conversion of the Gentiles, and were bringing great joy to all the brethren. 4And when they arrived at Jerusalem, they were received by the church and the apostles and the elders, and they reported all that God had done with them.