There is not really a “beyond” in Christian theology, given that everything that we learn in Sunday school is still true when systematic theology rears its dogmatic head. It is impossible to transcend the basics. Although there is a “mere Christianity” that all Christians hold in common, it is possible, nay, desirable to elaborate upon what we believe and develop smart Christianity. The question of whether the Holy Spirit proceeds from the Father only or from the Father and the Son together was one issue at stake in the East-West Schism of 1054. The Pope’s decision to tack “and from the Son” onto the end of “proceeds from the Father” in the Nicene Creed spiritually means something. The theology that we believe goes into the kind of people that we become. As learned Christians elaborate upon “mere” Christianity, they are not merely playing a game for bookworms.
In The Mystical Theology of the Eastern Church, Vladimir Lossky states,
If even now a political doctrine professed by the members of a party can so fashion their mentality as to produce a type of man distinguishable from other men by certain moral or psychical marks, a fortiori religious dogma succeeds in transforming the very souls of those who confess it. They are men different from other men, from those who have been formed by another dogmatic conception.
As Christians examine TULIP, papal supremacy, Arminian soteriology, and weigh the views of Christ’s divine-human composition, they make decisions about what kinds of people they are becoming. Belief Two builds upon Belief One, and believing that subtle distinctions in theology are just Star Trek vs. Star Wars arguments for nerds is in itself a Belief One that supports a Belief Two. What Christians do with people who disagree with them is in itself a spiritual decision. From the lady adding and subtracting dollars in the supermarket to the nuclear physicist playing with imaginary numbers in a top secret lab, while simple math is enough for practical matters, anyone looking at an Intercontinental Ballistic Missile in an exhibition lit by nuclear power knows that advanced math is also enough for practical matters.
Mere Christianity is powerful stuff. It helps Protestant and Catholic missionaries cooperate on the mission field to serve people with physical needs and leads Lutheran and Eastern Orthodox Christians to dig for their common roots. Even so, it is not an iron to press flat the various folds following the Good Shepherd. Transubstantiation is not just a funky Catholic idea, and the five Protestant “solas” as an expression of basic Christianity are not practically the same thing as the decisions handed down by the Council of Trent. Protestants and Catholics agreed in many areas as they reformed abuses in the Church, but Henry VIII’s Dissolution of the Monasteries revealed a Protestant fresh perspective on the sanctity of Church property. If I am an ecclesiological pluralist, it is as a pragmatic maneuver to keep peace with people who love God. Because I believe that Calvinism is wrong, I argue against it when it comes up in conversation, but I have enjoyed fellowship in Reformed churches because they possessed enormous stocks of mere Christianity.
When I find myself debating with Calvinists, I make better progress with them than when I chat with agnostics. My disagreements with atheists and agnostics are actually flat and uninteresting compared to my disputes with Calvinists because of the extent to which we agree. Arguments within the game of Monopoly are far more heated than discussions of whether the game is worth playing. When we quote St. Augustine as saying, “In essentials unity, in non-essentials liberty, in all things charity,” it is with the point of letting each other live long enough to make good progress in studying and obeying the truth. Even non-essentials matter, but we also believe that charity is true. Getting into advanced theology matters quite a bit, so when you have to let go of a position, be sure to do so as letting go of a lower rung to grasp a higher.