It might be easier to just read Article 4 of the Apology. If you doubt the importance of Romans 4 and the role of Paul in Lutheran theology, doubt no longer!

Psalm 121

The Lord will keep your going out and your coming in from this time on and forevermore.
— Psalm 121:8

Verse 8 is quoted in The Small Catechism, Baptismal Booklet with the citation given in a footnote (SC, 9.18, n. 160) . It is of some interest that we don't include this line in the baptismal rite anymore, but then the rite has been changed several times just within my lifetime. Reading around this area and in the footnotes shows how even this version in the Small Catechism presented changes.

Romans 4:1-5, 13-17

I hope it’s not a surprise that there are many citation of this reading, an inordinate number of which are in the Apology of the Augsburg Confession, Article 4: Justification. I’ll cover those as they come up in that article, then turn to a short argument in Article 12: Repentance in the same document that has three citations, follow that up with a visit to both parts of the Formula of Concord, Article 3: Righteousness, and then come back to the rest.

The Justification Argument

For if it is the adherents of the law who are to be the heirs, faith is null and the promise is void. For the law brings wrath, but where there is no law, neither is there transgression. For this reason the promise depends on faith, in order that it may rest on grace, so that it may be guaranteed to all his descendants, not only to the adherents of the law but also to those who share the faith of Abraham (who is the father of all of us, …
— Romans 4:14-16 (NRSVue)

As Melanchthon wraps up his argument against those who found fault with The Augsburg Confession, he quotes verse 15 (AP 4.38) to show that the Bible itself says that the law brings wrath. So how can following the law justify us if what it brings is wrath? It doesn’t. The law cannot justify us.

Melanchthon quotes verse 14 (AP 4.42) to show that if the law is how we are reconciled to God, then faith in God’s promise of forgiveness would not matter, because all we would have to do is follow the law to earn forgiveness. This idea Paul debunks in verse 14.

As he begins to present what the justifying faith is, Melanchthon quotes verse 16 (AP 4.50) to make the argument that God’s promise can only be received by faith.

For what does the scripture say? “Abraham believed God, and it was reckoned to him as righteousness.”
— Romans 4:3 (NRSVue)

Melanchthon partly quotes verse 3 (AP 4.58ish) to set up the argument that Abraham was justified by faith and not works.

As he connects the justifying faith to the forgiveness of sins, Melanchthon quotes verse 16 (AP 4.84) to show that the forgiveness of sin is a promise of God and so can only be received by faith, thus intimately connecting faith and forgiveness.

But to one who does not work but trusts him who justifies the ungodly, such faith is reckoned as righteousness.
— Romans 4:5

The editor calls out the citation of verse 5 (AP 4.86) so we can know where to go to see it clearly stated that faith is why God reckons us as righteous. The editor also notes the citation of verses 1 thru 6 (AP 4.87) as the place where Paul shows that both Abraham and David were justified by faith, and not by the work of circumcision, which they were both commanded to do by the law.

Melanchthon calls out the entirety of chapter 4 (AP 4.88) to show that Paul’s idea of “faith justifies” is not accidental, but a key part of his theology. He then goes on to quote verses 4 thru 5 (AP 4.89) and to drive home the central point that justification comes through faith and that faith is what is reckoned as righteousness, not the works.

Melanchthon comes back to verse 15 (AP 4.319ish) to argue that depending on the law to justify only leads the honest person into despair because they see their life through the law and how much they consistently fall short.

The Repentance Issue

Verses 15 thru 16 become come back up in the Apology of the Augsburg Confession, Article 12: Repentance.

For the law brings wrath, but where there is no law, neither is there transgression. For this reason the promise depends on faith, in order that it may rest on grace, so that it may be guaranteed to all his descendants, not only to the adherents of the law but also to those who share the faith of Abraham (who is the father of all of us, …
— Romans 4:15-16 (NRSVue)

Verse 16 comes up first (AP 12.61) as Melanchthon argues that “absolution is the promise of the forgiveness of sins,” and since it is a promise, then faith is what receives absolution and so must be part of repentance. Who would repent if they didn’t believe God’s promise of forgiveness? And then again (AP 12.81) to show that if we want to hold on to something as an assurance that our sins are forgiven, it must be faith that we hold on to and not the law. Melanchthon drives this home by quoting verse 15, because if we look to the law to discover that our sins are forgiven, we will only find God’s wrath.

Formula for Righteousness

Six citations from Romans 4 come up in the Formula of Concord.

First, verse 5 is quoted in the Epitome, Article 3: Righteousness, Affirmative Thesis 3 (FC, Ep 3.5), and makes it clear that only faith in Christ makes us righteous before God because of Christ’s righteousness.

Now turning to the Solid Declaration, verse 16 is part of a long list of citations from Romans, Galatians, and Ephesians (FC, SD 3.7), every one of which is an example of Paul excluding the law from the role of faith because faith is not itself a work that saves us. This is emphasized with an allusion to verse 5 a little later (FC, SD 3.12), which sets up the following:

For faith does not make people righteous because it is such a good work or such a fine virtue, but because it lays hold of and accepts the merit of Christ in the promise of the holy gospel.
— Formula of Concord, Solid Declaration,
Article 3: Righteousness (FC, SD 3.13)

God reckons us righteous because of faith, not because of the work of faith. This idea comes back later in the same article to drive home the point.

What then are we to say was gained by Abraham, our ancestor according to the flesh? … For what does the scripture say? “Abraham believed God, and it was reckoned to him as righteousness.” … But to one who does not work but trusts him who justifies the ungodly, such faith is reckoned as righteousness. So also David pronounces a blessing on those to whom God reckons righteousness apart from works…
— Romans 4:1, 3, 5-6

Verses 1, 3, and 5 thru 6 come up in quick succession (FC, SD 3.33 and 3.34) to point out that while Abraham did do many good works, the works are not why God reckoned him as righteous. Conversation about the saving faith and conversation about the good works that follow the saving faith should be kept separate so that the promise of God might indeed comfort troubled consciences.

Everything Else

Verse 5 is cited in The Augsburg Confession, Article 4: Justification (AP 4.3) to show the biblical grounding for the idea that justification is reckoned by God because of faith.

Verse 15 is quoted at the end of Smalcald Articles, Part 3, Article 2: Law (SA 3.2.5) as a reminder that the primary role of the law is to point out or sin.

Verse 16 is quoted in the Apology of the Augsburg Confession, Article 20: Good Works (AP 20.10) to clearly state what Melanchthon spent so much time addressing in Article 4: Justification. The certainty we have that our sins are forgiven is faith—believing that God will forgive us our sins. Works do not merit our forgiveness. If forgiveness is based on our work, how can we ever be sure we have done enough?

John 3:1-17

Jesus answered him, “Very truly, I tell you, no one can see the kingdom of God without being born from above.”
— John 3:3 (NRSVue)

Verse 3, along with verse 5 below, is cited in a footnote to The Small Catechism, Baptismal Booklet (SC 9.8, n. 150) to help enforce the significance of choosing faithful and upright sponsors and a faithful and upright priest for your child's baptism. Those who don't take baptism seriously miss God's own honoring of baptism as the new birth, being born again, or being born from above.

Jesus answered, “Very truly, I tell you, no one can enter the kingdom of God without being born of water and Spirit.
— John 3:5 (NRSVue)

Verse 5 is quoted in Apology of the Augsburg Confession, Article 4: Justification (AP 4.31) as a reminder that not even reason can be so righteous as to make us acceptable to God. We must be reborn in our entirety, including our reason.

Verse 5 is also cited in a footnote to The Small Catechism, Baptismal Booklet (SC 9.8, n. 150). See verse 3 above.

[Jesus said,] “And just as Moses lifted up the serpent in the wilderness, so must the Son of Man be lifted up, that whoever believes in him may have eternal life. For God so loved the world that he gave his only Son, so that everyone who believes in him may not perish but may have eternal life.”
— John 3:14-16 (NRSVue)

Verses 14 thru 16 along with verses 17 and 18 below are quoted in Apology of the Augsburg Confession, Article 4: Justification (AP 4.95) in a section where Melanchthon is quoting sections of scripture to make the point that the Bible itself presents the idea of justification by grace through faith.

Verse 16 is cited by itself in several places in Formula of Concord, Solid Declaration. The first instance is a quote in Article 2: Free Will (FC, SD 2.49) that serves as scriptural proof that, "It is not God's will that any are damned but that all turn to [God] and be saved."

Verse 16 is then partly quoted in Article 7: Holy Supper (FC, SD 7.70) as part of a thought about who is worthy to receive communion. This verse is used to show that what makes you worthy to receive is faith with no emphasis on the quality thereof.

The beginning of this verse is quoted twice in Article 11: Election. The first time (FC, SD 11.28) as a reminder that the promise of the gospel is for all people. The second time (FC, SD 11.67) as a reminder that salvation through Christ is God's will and enacted love.

[Jesus said,] “Indeed, God did not send the Son into the world to condemn the world but in order that the world might be saved through him. Those who believe in him are not condemned, but those who do not believe are condemned already because they have not believed in the name of the only Son of God.”
— John 3:17-18 (NRSVue)

This goes one verse beyond the assigned reading for the week, nevertheless verses 17 thru 18 are quoted twice in Apology of the Augsburg Confession, Article 4: Justification. The first quote (AP 4.96) is in the same section as verses 14 thru 16 above. The second quote (AP 4.333ish) to show that "mercy has the clear mandate of God. For the gospel itself is the mandate that commands us to believe that God wants to forgive and to save on account of Christ."

TheoThru

God wants all people to be saved. Salvation comes through faith, which holds onto God’s promises. None of this is works, although good works will flow from faith. The faith that saves is quite direct: believe that God forgives you all your sins because of Jesus. That’s it. Faith holds this promise close, and this faith that trusts God to keep promises is what God reckons to us as righteousness.

You are forgiven. Believe.

You are saved. Believe.

God loves you. Believe.