Christ and the Law can by No Means Agree

.....because they mingle the law with the Gospel, they must needs
be perverters of the Gospel.  For either Christ must remain, and
the law perish, or the law must remain and Christ perish; for Christ
and the law can by no means agree and reign together in the conscience.
Where the righteousness of the law ruleth, there cannot the righteousness
of grace rule; and again, where the righteousness of grace reigneth, there
cannot the righteousness of the law reign; for one of them must needs
give place unto the other.  And if thou canst not believe that God will
forgive thy sins for Christ's sake, whom he sent into the world to be
our high-priest; how then, I pray thee, wilt thou believe that he will
forgive the same for the works of the law, which thou couldest never
perform; or for thine own works, which (as thou must be constrained
to confess) be such, as it is impossible for them to countervail the
judgment of God?
     Wherefore, the doctrine of grace can by no means stand with
the doctrine of the law.  The one must simply be refused and
abolished, and the other confirmed and established.  For as Paul
saith here, to mingle the one with the other, is to overthrow the
Gospel of Christ.  And yet, if it come to debating, the greater
part overcometh the better; for Christ, with his side, is weak, and
the Gospel but a foolish preaching; contrariwise, the kingdom
of the world, and the devil, the prince thereof, are strong.
Besides that, the wisdom and righteousness of the flesh carry a
goodly show; and by this means, the righteousness of grace and
faith is lost, and the other righteousness of the law and works
advanced and maintained.....
     It seemeth to be a light matter to mingle the law and the
Gospel, faith and works, together:  but it doth more mischief
than a man's reason can conceive; for it doth not only blemish and
darken the knowledge of grace, but also it taketh away Christ,
with all his benefits, and it utterly overthroweth the Gospel, as
Paul saith in this place.  The cause of this great evil is our flesh,
which, being plunged in sins, seeth no way how to get out but by
works, and therefore it would live in the righteousness of the law,
and rest in the trust and confidence of her own works.  Wherefore,
it is utterly ignorant of the doctrine of faith and grace,
without the which, not withstanding, it is impossible for the conscience
to find rest and quietness....
.....So we at this day do not reject fasting, and other good exercises,
as damnable things; but we teach, that by these exercises we do not
obtain remission of sins.
                                              Martin Luther