With many canned Bible study curricula, it is sometimes more interesting to detect what passages of Scripture have been omitted than to study what is said about those passages that have not.
Occasionally these omissions are due to the theological/doctrinal bent of the writer, but sometimes merely reflect a lack of stomach to discuss hard truths that comfortable believers don't want to hear.
First Corinthians 5, which orders the excommunication of a sexually immoral man, is one of these passages. The study materials offered by a a prominent publishing house include 1Co5 in a section on "Christian Morality," but ignore any discussion of the entire chapter.
The discipline of members (the imperative) is inextricably bound up in the idea of who the church is, in Christ (the indicative). 'Cleanse out the old leaven that you may be a new lump, as you really are unleavened. For Christ, our Passover lamb, has been sacrificed' (1Co5:7 ESV).
The distinguishing characteristics of God's people in the Old Testament included radical devotion to a single God, demonstrated in strict dietary laws, sacrificial requirements, and, through the Passover, a sense of haste that mandated little time to wait on bread to rise.
Distinguishing characteristics of God's people -- that we are a 'new lump' -- have not been eradicated in the New Testament, but only modified: it is no longer ethnic identity that sets us apart, but grace and a life of obedience that flows from it ('And if you are Christ's, then you are Abraham's offspring, heirs according to promise' Gal3:29, ESV).
We are no longer set apart, but have become indistinguishable from the world, when we live like the world and tolerate sin ('of a kind that is not tolerated even among pagans' 1Co5:1 ESV). Our distinguishing characterstic is, of course, that we love one another (John13:35). But this love does not ignore the putrefying effects of unconfessed, unrepentant sin in the camp. Instead, it recognizes who we are in Christ, and in love seeks both to preserve the souls of men (1Co5:5) and to honor the name of Christ.