What Scripture shows you that legalism is defined in the way that you define it
Acts 15:1 Some men came down from Judea teaching the brethren, "Unless you are circumcised according to the custom of Moses, you cannot be saved."
Galatians 5:4 You have been severed from Christ, you who are seeking to be justified by law; you have fallen from grace.
To me, Galatians 5:4 is the cornerstone to understand Galatians. To assume anything else from Galatians is to cause Paul to talk out of both sides of his mouth.
Where does Scripture teach that legalism is the yoke being talked about?
Acts 15:10 "Now therefore why do you put God to the test by placing upon the neck of the disciples a yoke which neither our fathers nor we have been able to bear?
I hope this answers your questions, Dave Miller.
-- slade
