Luther rejoices in the doctrine of _sola gratia_ because it alone is
able to engender assurance of salvation. He writes: "As for myself, I
certainly confess that, if such a thing could somehow be, I should be
unwilling to have free will given me, or anything left in my own hand,
which might enable me to make an effort at salvation; not only because
in the midst of so many dangers and adversities and also of so many
assaulting devils I should not be strong enough to remain standing and
keep my hold of it (for one devil is mightier than all men put together,
and not a single man would be saved), but because, even if there were no
dangers and no adversities and no devils, I should still be compelled to
toil forever uncertainly, and to beat the air in my struggle. For though
I should live and work to eternity, my own conscience would never be
sure and at ease as to how much it ought to do in order to satisfy God.
No matter how perfect a work might be, there would be left a doubt
whether it pleased God, or whether He required anything more, as is
proved by the experience of all who endeavor to be saved by the Law
(_iustitiariorum_), and as I, to my own great misery, have learned
abundantly during so many years. But now, since God has taken my
salvation out of the hands of my will, and placed it into those of His
own and has promised to save me, not by my own work or running, but by
His grace and mercy, I feel perfectly secure, because He is faithful and
will not lie to me; moreover, He is powerful and great, so that neither
devils nor adversities can crush Him, or pluck me out of His hand. No
one, says He, shall pluck them out of My hand; for My Father, who gave
them unto Me, is greater than all. Thus it comes to pass that, though
not all are saved, at least some, nay, many are, whereas by the power of
free will absolutely none would be saved, but every one of us would be
lost. We are also certain and sure that we please God, not by the merit
of our own work, but by the favor of His mercy which He has promised us,
and that, if we have done less than we ought, or have done anything
amiss, He does not impute it to us, but, as a father, forgives and
amends it. Such is the boast of every saint in his God." (E. 362; St. L.
1961f.)
In the _Apology of the Augsburg Confession_ this thought of Luther's is
repeated as follows: "If the matter [our salvation] were to depend upon
our merits, the promise would be uncertain and useless, because we never
could determine when we would have sufficient merit. And this
experienced consciences can easily understand [and would not, for a
thousand worlds, have our salvation depend upon ourselves]." (CONC.
TRIGL. 145, 84; compare 1079, 45f.)