It is times like these that I REALLY appreciate my denomination's centering on the lectionary! It means that I cannot use the pulpit to hit people over the head. If there is an particularly apropos reading then I can blame it on the serendipity of the Holy Spirit; we can all smile and move on.
When emotions are high it is important to hear that God is still in this place, that peace is still possible and God is forgiving. Church fights are always 'family quarrels' and can be much more debilitating than any other disagreements. I would not preach prophetically in this case, but preach with the intent of healing, of the coming together of people who are hurt and looking for some salve for their woundedness. Do anything you can to dial down the emotions in the congregation. You can do this better than the pastor because he is evidently on one side.
In this case I would preach something about finding peace in the love of God. I would not use the Matthew 15 passage because you are not the pastor. The story of Elijah on the mountain after the whirlwind and God speaking in the still small voice might be good. Or perhaps even the story of Jacob and Esau reconciling after Jacob's stealing his birthright.
And Sharon offers:
Oh my goodness! You really can't make this stuff up, can you?
I would probably default to the Lectionary texts. I have found them to be rich sources of good news, perfectly timed for all kinds of weird situations. Using the appointed texts helps me rely more on the Holy Spirit than on my own decision-making and comfort levels. That said, if the Spirit is (or was) already leading you to another text, by all means go with that. Most (all?) of the Bible's background scenery is controversy and conflict, if not outright war. Even Bible hero Psalm-writing shepherd David had a dark side!
Can you also look for ways to bring in your faith tradition's values? In the UCC, for example, unity is a core value with both biblical and historical roots. Also, if you know anything about that church's history, or the history of the "neighborhood," I bet you will find something to share from that, too.
My prayers are most definitely with you!
Thank you so much, Matriarchs, for your thoughtful responses. What about the rest of you? Do you have advice for our colleague? Let's continue the conversation in the comments, and, as always, if you have a question you'd like the matriarchs to discuss, please send us an email at askthematriarch[at]gmail[dolt]com.