Galatians

Galatians — False teachers have infiltrated the churches in Galatia, falsely suggesting that works of the law (specifically circumcision) must be added to faith in Christ in order for salvation to be real. In no uncertain terms, Paul condemns the mixture of law and grace, showing that salvation and sanctification are all of grace. Christ’s salvation has set us free. We rely on the Spirit’s work, not our own.
Source: GotQuestions.org