While I appreciate your appeal for unity, the idea of "core essentials" cannot be found in Scripture. 1 Corinthians 1:10 claims followers of Christ must be agreed... that we must be united... that we must believe and speak the same thing. Ephesians 4:3 indicates that it doesn't come naturally - rather, we must make this an endeavor - something to be striving towards. Nothing, however, in those discussions lead a person to conclude there are only a few issues that must be agreed upon. Because people refuse to be unified, many people tell us today that everyone agreeing to lists like the one above (or a creed) must be OK... which leads to a watering down of what Jesus said in places like Matthew 5:19 and Matthew 28:20.