Okay, let's get uncomfortable. Think back to the last time you remember speaking roughly, unkindly, or rudely to someone. Didn't take long, did it? Now, who was the receipt of your deadly barrage (because, after all, the old rhyme is a lie: sticks and stones can break my bones, but words can break my heart!). My personal survey reveals the tragic fact that those who suffer harm from the infliction of my harsh words are my brothers and sisters in Christ.
Perhaps I am not the only one who tries, and usually succeeds, in guarding my tongue around the lost, for fear of compromising my testimony for the Lord. But the guard all too often comes down around Christian. That awareness draws me back to Galatians 6.:10 which records Paul admonishing followers of Christ to "as we have opportunity, let us do good to all people, especially to those who belong to the family of believers (emphasis added)." The Spirit of God prompts me to 1Thessalonians , which states "Make sure that nobody pays back wrong for wrong, but always try to be kind to each other and to everyone else." The "each other" is obviously a reference to the church, thus re-emphasizing the "especially" of the verse from Galatians.
As I survey, however painfully, my life I recognize that I have the most verbal failings around those who mean the most to me: my "blood" family and my "Blood (purchased by) family." Excuses are like elbows, everybody has a couple, but God does not forgive excuses, He forgives sins when we agree with Him that such failings are not "character weaknesses," "just the way I am," or "oops," but are sin (see 1 John 1:9).
It is not much comfort to recognize I am not alone. I occasionally filled in to answer the phones at a large ministry I served, and that can be traumatic as there are occasions when ticket seeker verbally assault the staff. Gratefully the vast majority of people were gracious, kind, and understanding. But others, apparently Christian, feel the clerk is personally responsible for sell-outs and let him/her know in words they'd hopefully never use in conversation with those "outside the faith." Others accused us of being "non-Christians" because we charge for tickets and try to maintain control of them.
Again, their choice of words and their reasoning is embarrassing. Wherever two or three are gathered, there will be conflicts. But I certainly need to strive to resolve any disagreements in a way that is in accordance with the clear commands of God, who tells me not to play the "but I'm a fellow Christian" card, nor to speak harshly, cruelly, or otherwise unkindly to anybody, "especially" to my fellow ambassadors of the Lord Jesus Christ.
How dare I speak to His representative in a harmful way! Too many years ago I thought Ephesians 4:29 was God's telegram direct to my heart. These many years later I've memorized the verse, but I have a devil of a time applying it with regularity that pleases me.....or Him. So, if you have a moment, pray that I'd obey that verse (look it up if you need to). And, perchance, maybe the Spirit of God will speak to you through His comforting yet cutting Word.