Every manner of unconfessed sin is inconsistent with communion at this table. But when the apostle comes to mention particular sins in conjunction with keeping our observance holy, it is notable which sins he singles out.
One of them is murmuring. Not only are we to avoid golden-calf-like idolatries, not only are we to avoid testing Christ, we are also told to set aside all complaining, all grumbling, all murmuring.
This means that our demeanor as we come to the Table is to be one of contentment. We are not permitted to grumble — even if the grumbling is over our sinfulness. He is the master of the feast; it is His business to invite, or not. If He has invited you, (and if you are baptized, He has), then it is your duty to come. And if you are not baptized, then you are invited to the water, and to the Table after.
But we know that as we call on His name in faith, the water washes sin away. Discontent is one of those things to be washed away. And this means every form of discontent. You are at His table, and must do what He says. Rest content then — in your marriage, in your finances, in your gifts, in your appearance, in your station, in your family, in your schoolwork, in your opportunities, in your trials, in your food, in your life.
You are seated now at His table. He looks around from His position at the head of the table and asks if everyone has washed up. In particular, He wants you to let Him wash away the grime of grumbling. If you have not done so, do not get up from the Table to go wash. Confess your discontent now, where you are seated. Let it go, now.