That we cannot be saved by circumcision and the Mosaic Law.
But don't think being saved by grace gives us license to live like we ain't saved. If we aren't believers enough to change our lives, then we need to question if we really are believes (and by extension aren't saved).
So we are not saved by faith alone: faith must be accompanied with changing our lives, i.e. good works.
That is actually how sola fide was described in no less a document than the Westminster confession:
Faith, thus receiving and resting on Christ and His righteousness, is the alone instrument of justification;(d) yet is it not alone in the person justified, but is ever accompanied with all other saving graces, and is no dead faith, but worketh by love.(e) - https://www.ligonier.org/learn/articles/westminster-confession-faith/
What Catholics seemingly cannot comprehend or allow is that is it the faith that will effect obedience that is counted for righteousness, but the effect is not the cause, the means of appropriation, even though they are two sides of the same coin.