Supper long post for this week, but the psalm brings it—particularly verse 1—and so does the second reading—particularly verse 21. All the ideas! Justification, prayer, forgiveness, communion, good works, contrition, election...

Psalm 32

Happy are those whose transgression is forgiven,
whose sin is covered.
— Psalm 32:1

Verse 1 is quoted in Apology of the Augsburg Confession, Article 4: Justification (AP 4.76) to show that the forgiveness of sins is the same thing as being justified to God.

This same verse is quoted later in the same article (AP 4.103) within a quote from a letter from Ambrose's to Irenaeus showing that it is faith in Jesus that frees us, not our works.

And again, later in the same article, this verse is quoted within a much larger argument of why love does not justify as part of the fourth point (AP 4.172), that "Christ does not stop being our mediator after we are reborn" (AP 4.172). Verse 1 shows that "we need the forgiveness of sins even when we have good works" (AP 4.172).

Verse 1 is also quoted in Formula of Concord, Epitome, Article 4: Good Works, Affirmative Thesis 3 (FC, Ep 4.7, n. 35) within a quote from Romans to show that "good works must be completely excluded from any question of salvation as well as from the article on our justification before God" (FC, Ep 4.7) because salvation comes through faith.

Then I acknowledged my sin to you,
and I did not hide my iniquity;
I said, “I will confess my transgressions to the Lord,”
and you forgave the guilt of my sin.
— Psalm 32:5

Verse 5 is quoted in Apology of the Augsburg Confession, Article 12: Repentance (AP 12.107) to show that "when confession is made to God, it is of necessity made with heart and not simply with the mouth, as is done by actors on the stage. Therefore such a confession is contrition" (AP 12.107).

Therefore let all who are faithful
offer prayer to you;
at a time of distress, the rush of mighty waters
shall not reach them.
— Psalm 32:6

Verse 6 is also quoted in Apology of the Augsburg Confession, Article 4: Justification (AP 4.148) within the larger argument of verse 1 to show that those who are faithful "pray for the forgiveness of sins" (AP 4.148) because faith shows us that we cannot keep the law.

2 Corinthians 5:16-21

So if anyone is in Christ, there is a new creation: everything old has passed away; see, everything has become new!
— 2 Corinthians 5:17

Verse 17 comes up in Formula of Concord, Solid Declaration, Article 2: Free Will (FC, SD 2.26) as a passing citation among a list of citations showing that faith and everything involved therein--here, making us new creatures--is totally and completely (FC, SD 2.25) the work of the Spirit.

…that is, in Christ God was reconciling the world to himself, not counting their trespasses against them, and entrusting the message of reconciliation to us. So we are ambassadors for Christ, since God is making his appeal through us; we entreat you on behalf of Christ, be reconciled to God. For our sake he made him to be sin who knew no sin, so that in him we might become the righteousness of God.
— 2 Corinthians 5:19-21

Verses 19 thru 21 are cited together in Formula of Concord, Solid Declaration, Article 3: Righteousness (FC, SD 3.30) as editorial insert along with a passage from Romans 4 as scriptural references for defining justification in a particular and important way:

"In order that the troubled heart may have a reliable and certain comfort and that Christ's merit and God's grace may be given the honor due them, Scripture teaches that the righteousness of faith before God consists only in the gracious reconciliation or forgiveness of sins."
— Formula of Concord, Solid Declaration,
Article 3:, Line 30

Verse 19 by itself comes up in Formula of Concord, Solid Declaration, Article 7: Holy Supper (FC, SD 7.36) where it is cited with several other passages to make the argument against transubstantiation.

"Just as in Christ two distinct, unaltered natures are inseparably united, so in the Holy Supper two essences, the natural bread and the true natural body of Christ, are present together here on earth in the action of the sacrament, as it was instituted."
— Formula of Concord, Solid Declaration,
Article 7, line 37

Verse 20 by itself is quoted directly in Apology of the Augsburg Confession, Article 24: The Mass (AP 24.80) to show that the word "liturgy" is appropriate to describe "Communion" or "the Mass" because liturgy

"does not properly mean a sacrifice but rather a public service. Thus, it agrees quite well with our position, namely, that the one minister who consecrates gives the body and blood of the Lord to the rest of the people, just as a minister who preaches sets forth the gospel to the people."
— Apology of the Augsburg Confession,
Article 24, Line 80

Verse 20 comes up again in Formula of Concord, Solid Declaration, Article 11: Election (FC, SD 11.27) as a direct quote to show that when it comes to election, we can find comfort because repentance is to be preached to all people.

Verse 21 appears in Formula of Concord, Epitome, Article 3: Righteousness (FC, Ep 3.1) as a passing reference to the two natures of Jesus.

It should be no surprise, then that verse 21 also appears in Formula of Concord, Solid Declaration, Article 3: Righteousness (FC, SD 3.54) as an editorial insert citing Paul's writings in the argument that the

"indwelling of God is not the righteousness of faith, which St. Paul treats and calls iustitia Dei (that is, the righteousness of God), for the sake of which we are pronounced righteous before God. Rather, this indwelling is a result of the righteousness of faith which precedes it, and this righteousness [of faith] is nothing else than the forgiveness of sins and the acceptance of poor sinners by grace, only because of Christ's obedience and merit."
— Formula of Concord, Solid Declaration,
Article 3, Line 54
(Italics, parenthesis, and brackets in source)

But wait, verse 21 again appears in Formula of Concord, Solid Declaration, Article 5: Law and Gospel (FC, SD 5.22) as a direct quote in a list arguing that "all repentant sinners should believe in, that is, place their trust alone in, the Lord Christ," because "there is a vast difference between the knowledge of God that comes from the gospel and that which is taught and learned through the law" (FC, SD 5.22).

And verse 21 also shows up in Formula of Concord, Solid Declaration, Article 11: Election (FC, SD 11.15) as an editorial insert with several other passages in the first point of the list of points to help us ponder God's preordaining to show "That the human race has been truly redeemed and reconciled with God through Christ, who has merited with his innocent obedience, suffering, and death both the righteousness that avails before God and eternal life" (FC, SD 11.15).

Luke 15:1-3, 11b-32

And the Pharisees and the scribes were grumbling and saying, “This fellow welcomes sinners and eats with them.”
— Like 15:2

Verse 2 shows up in Smalcald Articles, Part 3, Article 2: Concerning the Law (SA 3.2.4, n.81) as an editorial footnote providing scriptural reference for how those who look to the law to justify before God "murmur" against God as they become "enemies of God."

TheoThru

Given the gospel reading, its probably most productive to focus on the connection between forgiveness of sin, justification, and reconciliation. But there are many ways one could go with all these citations.

How do we prepare ourselves to be reconciled to God only to be surprised by God's mercy and grace?
How do we ensure that Christ's merit and God's grace are given the honor due them?
How might we better enter into our public service so that other might experience God's call to repentance?