What is the Law?

…if you let yourselves be circumcised, Christ will be of no value to you at all…You who are trying to be justified by law have been alienated from Christ; you have fallen away from
grace.

- Galatians 5:2, 4

What is the law to us today? What do we rely on to affirm our righteousness to ourselves? Is it a specific behavior or action, or a state of heart in which a behavior or action is performed?