You might also be interested to read John Frame’s new autobiography: Theology of My Life. Having read his books for many years and been his “student” (yet without ever having met him) it was helpful to pair a life with a theology. The book narrates his growing up, attending Princeton and getting involved with the evangelicals there, and then his life in Philadelphia, Escondido, and finally Florida. Frame is a good egg.
The biggest barrier to on-the-ground ecumenism is when we take a system (like classical theism) and, by it, cause statements that the bible makes repeatedly to sound in need of defense, explanation, or counterintuitive clarification. Our theology should be so harmonious with the bible that when those steeped in our theology read the scriptures, they find far more things that elicit nods than frowns.
Update, 12/3/2017 – Frame posted a few more articles about this topic, due to some responses he has received: