"By this all people will know that you are my disciples, if you have love for one another." (John 13:35)
The way the world is meant to identify us is not our doctrine. Believe the doctrine, stake your life on it, defend it in any room; but Jesus, on the last night, with hours left, did not say they will know you by the accuracy of your theology. He said they will know you by how you treat each other. Which is a terrifying standard, because it means an outsider is qualified to grade us. They do not need seminary to run the test. They can run it in the parking lot after a business meeting, or by watching how the long-time members talk about the new family, or on a comment thread in about four seconds.
And they do run it, constantly. And here is what should break our hearts. Most of the people who have written off the church did not do it because they read something and disagreed. They did it because they watched something. They saw how we handled a disagreement, how we treated the one who left, how we spoke of the people not in the room, and they concluded that whatever we have, they do not want it.
The warmth is the apologetic. There is not a second one. Your carefully correct arguments are not what the watching world weighs; it weighs the love, or the lack of it, between the people who hold those arguments. So guard the doctrine, yes, and then know that the world will never get to it unless it can first get past how you love. Love one another as though the whole case for Christ depended on it, because to the people watching, it does.