Here are two jewels:
Augsburg Confession, Article IV, Justification:
Also they teach that men cannot be justified before God by their own strength, merits, or works, but are freely justified for 2] Christ's sake, through faith, when they believe that they are received into favor, and that their sins are forgiven for Christ's sake, who, by His death, has made satisfaction for our sins. 3] This faith God imputes for righteousness in His sight. Rom. 3 and 4.
Formula of Concord, Solid Declaration, Law and Gospel, paragraph 21:
For everything that comforts, that offers the favor and grace of God to transgressors of the Law, is, and is properly called, the Gospel, a good and joyful message that God will not punish sins, but forgive them for Christ's sake.
What's the gospel?
A good and joyful message of forgiveness to transgressors of the law.
How and when are said transgressors of the law freely justified?
When they believe that they are received into favor, and that their sins are forgiven for Christ's sake, who, by His death, has made satisfaction for our sins.
It's pretty clear what Book of Concord Lutherans believe. At least according to the Book of Concord. And the Scriptures.
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Here's a copy of Schmid's Doctrinal Outline in Microsoft Word format,
https://community.logos.com/forums/t/49680.aspx
May be of use to you.
