6 It is difficult to know if this looks back or forward or both. The warning suggests it looks back. For this verb, see Luke 8:18; 12:1, 15; 20:46; 21:8, 34. The present imperative reflects an ongoing spirit of watchfulness.
7 Both the “if” clause in this verse and the “if” clause in v. 4 are third class conditions in Greek.
8 Here the term “brother” means “fellow believer” or “fellow Christian” (cf. ἀδελφός 2.a, contra 2.c), but with a familial connotation. It refers equally to men, women, or children. However, because of the familial connotations, “brother” has been retained in the translation here in preference to the more generic “fellow believer” (“fellow Christian” would be anachronistic in this context).
9 Grk “And if.” Here καί (kai) has not been translated because of differences between Greek and English style.

In other versions

Pay attention to yourselves! If your brother sins, rebuke him, and if he repents, forgive him,

So watch yourselves.

“If your brother or sister sins against you, rebuke them; and if they repent, forgive them.

Be on your guard. If your brother sins, rebuke him, and if he repents, forgive him.

So watch yourselves!

“If another believer sins, rebuke that person; then if there is repentance, forgive.

“Be concerned about yourselves! If your brother sins, rebuke him, and if he repents, forgive him.

Take heed to yourselves: If thy brother trespass against thee, rebuke him; and if he repent, forgive him.

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