Go beyond carries the thought of passing over the line that divides right from wrong. The present tense with the negative has the force of that there be no going beyond. Thus Paul asserted that sexual sin doesn't just affect the one who is impure, but it violates the lives of others as well. The verb translated wrong has the root meaning of to have more, and so is used to mean to take advantage of, to defraud, to cheat. The present tense prohibits the continuation of such a practice.
Brother refers to the husband of any woman with whom one had an adulterous affair.
In any matter applies this instruction to any occurrence of moral impurity. A confirmation of the calling to holiness as a lifestyle is found in verse 7. Immorality must be avoided because it is inconsistent with God's gracious call to salvation. God is the one who issued the call. Ye were called brings out the fact that God took the initiative in bringing men to salvation.