The Necessity of Good Works

But in this connection [that good works are necessary, and that it is necessary to do good] the following distinction must also be noted, namely, that the meaning must be: a necessity of Christ's ordinance, command, and will, and of our obligation, but not a necessity of coercion.  That is: when this word necessary is employed, it should be understood not of coercion, but only of the ordinance of the immutable will of God, whose debtors we are.  His commandment points out that the creature should be obedient to its Creator.  For in other places (2 Cor 9:7, Philemon 14, 1 Pet 5:2),  something is termed of necessity which is wrung from one against his will, by force or otherwise, so that he acts externally for appearance, but nevertheless without and against his will.  For such hypocritical works God does not want, but the people of the New Testament are to be a willing people (Ps 110:3), and sacrifice freely (Ps 54:6), not grudgingly or of necessity, but are to be obedient from the heart (2 Cor 9:7; Rom 6:17).  For God loves a cheerful giver (2 Cor 9:7).  In this understanding and in such sense it is correctly said and taught that truly good works should be done willingly or from a voluntary spirit by those whom the Son of God has made free, even as it was especially for this opinion that the dispute concerning the voluntariness of good works was engaged in by some.

But here, again, it is well to note also the distinction of which Paul says:

For I delight in the law of God, in my inner being, but I see in my members another law waging war against the law of my mind (Rom 7:22-23)

And as regards the unwilling and rebellious flesh, Paul says:

But I discipline my body and keep it under control (1 Cor 9:27)

and:

And those who belong to Christ Jesus have crucified the flesh with its passions and desires (Gal 5:24; Rom 8:13)

But it is false, and must be censured, when it is asserted and taught as though good works were free to believers in the sense that it were optional with them to do or to omit them, or that they might or could act contrary to [God's law], and none the less could retain faith and God's favor and grace.

Solid Declaration of the Formula of Concord IV 16-20