Antinomianism is simply the other side of Legalism.
It can be a bit more nuanced than that though I believe. Some antinomians believe that the
necessity of obedience of the moral law is a legalistic concept, such that it’s held to be wrong to teach an obligation to obey the Ten Commandments. And reasonably or not that position can apparently arise from the doctrine of Sola Fide as demonstrated by some on this thread I believe.
It’s related to the reason why many insist that Catholicism teaches a works-based salvation or why they cannot reconcile the prima facie reading of Romans 2:13,
“For it is not the hearers of the law who are righteous before God, but the doers of the law who will be justified. “
with Rom 3:28
“
For we hold that one is justified by faith apart from works of the law”.
It’s related to the reason why some argue that man is no longer obligated, with eternal life at stake, to be personally righteous under the New Covenant. Since a strictly imputed righteousness is said to make one righteous in the eyes of God, then any obligation to be
actually righteous can be seen as not only superfluous, but prideful and arrogant, negating the work of Christ by supplanting it with our own. But Catholicism teaches that only
because of the work of Christ is man now finally
equipped to work too, but not with works of the law, which exclude Christ, but with works of grace, works of love, which are only possible with and because of Him.
So, thus freely and gratuitously equipped at justification, now with the Spirit who pours out love into our hearts, we can work out our salvation with He who works in us.
God's Law is serious and real, and we are to do it. Not as though we can earn our way into paradise; but because as God's people it's what we ought to be doing. Not by fretting over the things of the Torah which don't even apply anymore, but rather that in faith we fulfill the law in this one word, "You shall love your neighbor as yourself" (
Galatians 5:14). Thus the righteousness of the Law is fulfilled not by works, but by faith; and faith is at work in love.
But is it what "we ought to be doing" because it's not only simply
right to do but also because without such righteous living one cannot enter heaven (a very Scriptural assertion in any case)? And we know that love fulfills the law but I'm not sure we can link faith
directly to that fulfillment even though it's absolutely necessary as the basis. In historical teachings I'm familiar with, FWIW, one can have faith without having love but love always encompasses the other virtues, of faith and hope. It may seem like hair-splitting but with the differing opinions on what it means to be justified-and of what is required of man- I'm not sure that this understanding isn't helpful, as well as consistent with 1 Cor 13 incidentally.
Either way in his statement Luther links faith-and the justification it obtains- with personal righteousness; we can't claim to have one unless we have the other, even if personal righteousness still involves choice and struggle, with failure to be expected at times, and then a contrite and repentant heart necessary to restore us to right relationship with God who's always calling us back to Himself with the open arms of forgiveness and love. In Catholicism this personal righteousness, obtained and exercised and expressed and grown and otherwise possessed to whatever degree God deems sufficient and appropriate for us an an individual, is required for salvation. Only love can fulfill the Law, and yet the Law
must be fulfilled by love. It just happens that, to the extent that we really
do love, obedience comes freely and willingly, of its own accord-and our obligation is thus satisfied, and without even needing to
hear the Law.
Anyway, the primary difference between the old and new covenants isn't with our obligation to be personally righteous-that remains. The difference is that, with the new covenant it's recognized that this can only occur
in partnership with God, entered into via faith, not on my own.
“
I will put my law in their minds
and write it on their hearts.
I will be their God,
and they will be my people." Jer 31:33