Rebuke of sin

I'm having a difficult time with a potential issue regarding those leading a worship service, including the pastoral office. Hypothetically, if a worship leader (layperson - singing or playing) is actively playing a role in a congregation, but a member/multiple members know that the leader is involved in a continual sin (examples: living with someone outside of marriage, addiction issues) unbeknownst to other church leadership, how does one act? If I'm helping to lead the service as well, do I use Matthew 18 and talk to them first, then with others? Do I move swiftly to church leadership to address the issue? I've had conflicting advice given on this (yes - leaders in worship are held to the same standard as pastors, and no - we are all sinners, so let it go). I don't like feeling like a tattle-tale, but I also don't like feeling smug like a Pharisee either. It has given me anxiety for a long time, and I'd like some clarification on this from a WELS leader. Thanks.

Matthew 18:15-20 provides direction for addressing sin in the lives of fellow Christians. That direction includes speaking to a fellow Christian individually and then widening the number of people involved if there is continued impenitence.

With your hypothetical situation, you would want to speak to the worship leader first—individually and privately. You would bring in others to assist you if there were continued impenitence.

We do not help fellow Christians if we fail to offer rebuke in Christian love when they sin. In fact, we help them greatly when we do speak to them—in humility and with gentleness—about their sins. The book of James ends on this note: “Remember this: Whoever turns a sinner from the error of their way will save them from death and cover over a multitude of sins” (James 5:20).

As you and I would want a fellow Christian to rebuke us about our sins, so we want to have a similar attitude toward a fellow Christian who is “involved in a continual sin,” as you described the situation. God grant you wisdom, love and strength.