Or what indeed has New York City to do with Königsberg?
In the last few years I've been sticking my nose into works of philosophy. Although seminary was a heady exposure to deep stacks of theology I never anticipated but deeply loved, I've come to believe that theology has much to learn in its continuing engagement with philosophical discourse.
The tricky thing about theology--it always seems to wend its way back to foundational authors or periods. Almost all contemporary philosophy, at least most philosophy written in Europe or in English, eventually has to engage those Germans like Hegel and Kant because they "changed everything."
Much the same can be said of a few German philosophers of the 20th century, Heidegger in particular. As uncomfortable as we are with Heidegger's politics, it's pretty difficult to get around engaging Heidegger. Similarly, if you want to do political theology, you have to come up against the juridical philosophy of Karl Schmitt.
In point of fact, as Jacob Taubes points out, Schmitt's work on political theology (infused as it was with anti-Semitism) was influential even in the drafting of the Israeli constitution.
In Christian theology, we have this anxiety of influence of a peculiar kind--basically all of our theology has been formed in conversation with the philosophy of the Greeks (the Church Fathers engaged Plato and Aristotle as an alternative to and denunciation of the mythology and liturgies of Greek mythology; Thomas Aquinas organized Christian theology around Aristotelian metaphysical categories).
So as early as Tertullian, Christian theologians were engaging Greek metaphysics and wedding it to the biblical worldview, while all the time questioning the enterprise.
As a reader whose impulse at least quite a bit of the time is to engage the footnotes, to dig down into sources, to consider how and why concepts emerge, I sometimes end up frustrated. Is it really the case that in order to think about philosophy in an era of post-colonialism and globalization, do I really still have to go back to Kant and Hegel? To think about the philosophy of technology, can't I dig into some other source than Heidegger?
The Unavoidability of Influence
The answer, unfortunately, is no. Some of these sources are so influential, so embedded in all our discourse and thinking, that there simply is no end run around them. One can only go through and beyond them, and continually back to them.
The issue with the original question of Tertullian--"What indeed has Athens to do with Jerusalem?"--is essential if complicated. As posed, the question implies that one can distinguish between a pure Athens and a pure Jerusalem. Athens represents a uniform Greek philosophy. Jerusalem represents a completely separate and distinguishable Hebraic worldview.
But are the two so distinguishable? Wasn't Jerusalem a meeting place for many cultures? Remember the Pentecost event, where Jews from many nations were gathered for trade and witnessed a new wind of the Spirit speaking through the disciples. Even prior to this, Hebrew culture was always infused and mingled with neighboring religions and thought-forms. From Solomon's wives to the exile in Babylon, from the references in Genesis to other early ancient texts to the Greek shift in the apocrypha (not to mention the transition from the Hebrew bible to the Septuagint as the primary source for theological reflection even among Jewish theologians), Greek and Hebrew culture were always already overlapping well before the Church Fathers began reading Aristotle.
Similarly, wasn't Athens a meeting place of many faiths? Paul tours the city and discovers shrines to so many gods that one shrine is even set up to an unknown god. And as already mentioned, Greek philosophy itself was not homogenous. Some types of philosophy were worked out in the theater and the temples, the philosophy of the gods and the tragedies. Another world of thought developed among the pre-Socratic philosophers and the three great philosophers, Socrates, Plato, and Aristotle (and perhaps also Plotinus).
The Danger of Influence
There are some dangers of unrecognized influence. The newer of the philosophies, the one brought into to contemporize the original, can risk co-opting the center of the philosophy one is trying to pristinate. This is a concern in many contexts. For example, post-colonial philosophers are rightly concerned that continual reference to European philosophy is a continuation of colonialism. After the Shoah, we are right to be concerned about the continuing of influence of anti-Semitism and National Socialism in the philosophy of Heidegger.
Or in a more modern context, to what degree should we be concerned about the life and values of the authors we read, such as the problem of John Howard Yoder's abuses in relationship to his pacifist theology, not to mention his influence on many theologians who have come after him?
So the awareness of influence is critical. But along with awareness should come the recognition that avoiding influence is impossible. It is how we live into influence that matters, rather than the whether of influence.
This is how Christianity works
One of the unique marks of Christianity is its translatability. The Bible, the Scripture of our tradition, existed as a holy book first in Hebrew, then in Greek, and later even in Latin. Over time, it has been translated into most of the world's languages, and that translation work is ongoing. Some of our best global theologians recognize translation as a crucial mark of our faith.
Indigenizaton of the faith is central to the spread of Christianity throughout the world, but indigenization has never functioned well by abandoning the cultural underpinnings of the Christianity being indigenized. For example, although there was some talk in the early church about dropping the Old Testament as Scripture, this heresy (Marcionism) was finally rejected by the church, because the church councils recognized that it was the cultural interplay between the older Scriptures and the newer Greek writings that was itself essential to a robust Christian theology.
You can't just replace a culture with Christianity, or add it onto it. Rather, Christianity develops within a new culture as gospel because it was already an intercultural conversation before it ever engaged a new culture in faithful and missionary conversation.
So when Scripture is translated well into new cultures, translators don't bracket off the New Testament and tack it onto the scriptures of the cultures into which they are translating (although some have attempted this). Instead, translators bring the Scriptures as a whole to the communities, and it is the interplay of Jerusalem and Athens, then in conversation with the third culture into which the faith is being translated, that becomes the living dynamic of the faith as it reaches more and more nations.
Canon, Creed, and the Development of Doctrine
All of this is very important because each form of Christianity we experience today, without exception, is a living tradition precisely because Athens and Jerusalem do have something to do with each other. In Western Christianity, this is primarily through the reciprocal developmental relationship between the canon (Scripture) and the creed. In this understanding, the creeds are not abusive expropriation of Scripture as accommodation to Western modes of thinking. Instead, they are the very way Scripture is lived and indigenized in the culture.
This is why, over time, Christianity was able to move to new centers, from Athens to Rome, from Jerusalem to Constantinople, from Constantinople to the third Rome, Moscow. And now we might add, to great Christian cities of the global south, like Buenos Ares or Lagos. There is not a higher, more universal Christianity to which we can appeal that transcends these specific places. Even Christian traditions in North America who believe they "just read the Bible" still have centers for their theological developments, such as Dallas, or Pasadena.
Doctrine develops in and through these specific places, not above them. Philosophy is always the philosophy of somebody, some school, not a transcendent sphere above the fray of cultural engagements. Every philosophy has not only authors, but cities.
Back to Philosophy
So why does this matter? Well, for one, because nobody made a better run at developing a philosophy of technology than Heidegger, and he did so by engaging the philosophy of the Greeks. You can consider technology by way of other philosophers, but you'll be lacking an important dialogue partner. Contemporary theologians considering technology in religious perspective acknowledge this, and work with Heidegger's thought. Perhaps the preeminent example currently is Brian Brock's Christian Ethics in a Technological Age.
Similarly, many philosophers and theologians attempting to navigate the shift to a post-secular society know that part of their work is continual engagement with the philosophers who created the conditions for the possibility of modern secularities, especially Hegel and Kant. So Roger Scruton's recent work, The Soul of the World, on the sacred in face of atheist options, engages Hegel in almost every chapter. He didn't set out to write a book about Hegel. But his project is best accomplished with Hegel as continual lodestar.
Personally, I'm particularly interested in this history of influence because I am captivated by the notion that we are now living in a world of multiple secularities, so indigenization of Christian faith in secularit(ies) entails close attention to the philosophers who first assisted in distinguishing the secular from the sacred, and then perpetuated or even deepened the tendency.
We simply cannot pretend that post-secularity isn't upon us. This isn't an option. The only option is to consider what it means to live in a world where various religious and secular options really are that for us, options.
Remembering Tertullian, I agree with James McGrath, who observes, "Tertullian himself provides a wonderful example of the fact that denying a connection puts one in a situation in which one is likely to make just such a connection without realizing it." Similarly, I think attempts to do philosophy without reference to the Greeks, or theology without reference to the influence of Athens, is likely to accomplish making such connections without realizing it.