From the Apology (Defense) of the Augsburg Confession, article V, paragraphs 113 and following. You can read the whole thing at the Book of Concord web site.
On the other hand, perfection, i. e the integrity of the Church, is preserved, when the strong bear with the weak, when the people take in good part some faults in the conduct of their teachers [have patience also with their preachers], when the bishops make some allowances for the weakness of the people [know how to exercise forbearance to the people, according to circumstances, with respect to all kinds of weaknesses and faults]. 114] Of these precepts of equity the books of all the wise are full, namely, that in every-day life we should make many allowances mutually for the sake of common tranquillity. And of this Paul frequently teaches both here and elsewhere. Wherefore the adversaries argue indiscreetly from. the term “perfection” that love justifies, while Paul speaks of common integrity and tranquillity. And thus Ambrose interprets this passage: Just as a building is said to be perfect or entire when all its parts are fitly joined together with one another. 115] Moreover, it is disgraceful for the adversaries to preach so much concerning love while they nowhere exhibit it. What are they now doing? They are rending asunder churches, they are writing laws in blood, and are proposing to the most clement prince, the Emperor, that these should be promulgated; they are slaughtering priests and other good men, if any one have [even] slightly intimated that he does not entirely approve some manifest abuse. [They wish all dead who say a single word against their godless doctrine.] These things are not consistent with those declamations of love, which if the adversaries would follow, the churches would be tranquil and the state have peace. For these tumults would be quieted if the adversaries would not insist with too much bitterness [from sheer vengeful spite and pharisaical envy, against the truth which they have perceived] upon certain traditions, useless for godliness, most of which not even those very persons observe who most earnestly defend them. But they easily forgive themselves, and yet do not likewise forgive others according to the passage in the poet: I forgive myself, Maevius said. 116] But this is very far distant from those encomiums of love which they here recite from Paul, nor do they understand the word any more than the walls which give it back. 117] From Peter they cite also this sentence, 1 Pet. 4:8: Charity shall cover the multitude of sins. It is evident that also Peter speaks of love towards one’s neighbor, because he joins this passage to the precept by which he commands that they should love one another. Neither could it have come into the mind of any apostle that our love overcomes sin and death; that love is the propitiation on account of which to the exclusion of Christ as Mediator, God is reconciled; that love is righteousness without Christ as Mediator. For this love, if there would be any, would be a righteousness of the Law, and not of the Gospel, which promises to us reconciliation and righteousness if we believe that, for the sake of Christ as Propitiator, the Father has been reconciled, and that the merits of Christ are bestowed upon us. 118] Peter, accordingly, urges us, a little before, to come to Christ that we may be built upon Christ. And he adds, 1 Pet. 2:4-6: He that believeth on Him shall not be confounded. When God judges and convicts us, our love does not free us from confusion [from our works and lives, we truly suffer shame]. But faith in Christ liberates us in these fears, because we know that for Christ’s sake we are forgiven.
119] Besides, this sentence concerning love is derived from Prov. 10:12, where the antithesis clearly shows how it ought to be understood: Hatred stirreth up strifes; but love covereth all sins. 120] It teaches precisely the same thing as that passage of Paul taken from Colossians, that if any dissensions would occur they should be moderated and settled by our equitable and lenient conduct. Dissensions, it says, increase by means of hatred, as we often see that from the most trifling offenses tragedies arise [from the smallest sparks a great conflagration arises]. Certain trifling offenses occurred between Caius Caesar and Pompey, in which, if the one had yielded a very little to the other, civil war would not have arisen. But while each indulged his own hatred, from a matter of no account the greatest commotions arose. 121] And many heresies have arisen in the Church only from the hatred of the teachers. Therefore it does not refer to a person’s own faults, but to the faults of others, when it says: Charity covereth sins, namely, those of others, and that, too, among men, i.e., even though these offenses occur, yet love overlooks them, forgives, yields, and does not carry all things to the extremity of justice. Peter, therefore, does not mean that love merits in God’s sight the remission of sins, that it is a propitiation to the exclusion of Christ as Mediator, that it regenerates and justifies, but that it is not morose, harsh, intractable towards men, that it overlooks some mistakes of its friends, that it takes in good part even the harsher manners of others, just as the well-known maxim enjoins: Know, but do not hate, the manners of a friend. 122] Nor was it without design that the apostle taught so frequently concerning this office what the philosophers call ejpieivkeian, leniency. For this virtue is necessary for retaining public harmony [in the Church and the civil government], which cannot last unless pastors and Churches mutually overlook and pardon many things [if they want to be extremely particular about every defect, and do not allow many things to flow by without noticing them]