From a recent exchange I had on Facebook with a universalist:
You have an undisciplined way of mixing and matching disparate passages. For instance, Jn 15:13 isn't about love in general. To the contrary, it's specifically about selective love: what we do for friends. That stands in implicit contrast to a stranger, passing acquaintance, or even a neighbor.
It's revealing to see how you filter passages through your universalism. Jn 15:13 trades on the fact that friendship is selective. A paradigm-case of selective love. That's why Jesus uses this example, because the connotations are universally accessible.
We love some people more than others. We love friends more than strangers. Which, btw, doesn't mean we hate strangers. But there are degrees of affection or compassion.
The whole force of Jn 15:13 lies in the implicit contrast between the special loves one has for friends in comparison to those who don't belong to that inner circle. Jesus is appealing to the universal intuition that we will do things for the sake of a friend that we wouldn't do for anyone else. Indeed, if we did it for everyone, there'd be nothing special about friendship. That would cheapen friendship beyond recognition.
In fact, the sacrificial love that one is prepared to make on behalf of a friend is a defining mark of friendship, which sets is apart from most other social relations.
"Didn't Jesus lay down His life for everyone—even strangers, passing acquaintances, & neighbors?"
Jesus is using an analogy. Sure, there's a sense in which Jesus dies for strangers. He dies for people who weren't even born at the time of the Crucifixion. He dies for people he didn't know in his lifetime (humanly speaking).
But that misses the point. He dies for people who are analogous to friends. And that implies selective love.
One of your problems is that you seem to operate with a concordance style associative methodology, where you take a word from one author in one context, take the same word from another author in another context, then use these unrelated passages to interpret each other. So, for instance, you use Rom 12:15 to interpret Rev 21:4. But to begin with, you haven't even established that Rom 12:15 has reference to mourning with mourners in general, rather than Christians mourning with fellow Christians in particular.
In addition, Rom 12:15 wasn't written with Rev 21:4 in view. Likewise, John didn't have Rom 12:15 in mind when he wrote Rev 21:4. You've introduced an idea into Rev 21:4 from (your interpretation of) Rom 12:15. That idea isn't present in Rev 21:4. You have a habit of importing ideas from one passage into an unrelated passage, then reinterpreting the second passage with that additional frame of reference. But that's illicit.