Adolf von Harnack, I think, has an underlying impact on me in ways that are greater than I’d like to admit. I came under this influence through my seminary training in an evangelical institution. I don’t think I’m the only one who has been subjected to this influence; indeed, 
most of the 20th century Anglophone (and of course Europhone) theological landscape has been shaped, one way or the other by this influence. The basic premise of Harnack is that the Gospel, early on in the Patristic period, was Hellenized, to the point that the canonical God of Hebrew orientation was syncretized and lost to the ‘god of the philosophers.’ I would say at some level two of my ‘favoritist’ theologians, Karl Barth and TF Torrance, have operated under this influence; i.e. the influence we see in the modern period in the ‘mediating theologians’ that gives us post or anti-metaphysical theologies. I am prone towards these sorts of theologies; the narratival theologies of Barth, and to a degree, even Robert Jenson.
Paul Hinlicky in his book Luther and the Beloved Community, as he is attempting to see how William James’s thought maps onto Martin Luther’s, has some insightful treatment on Harnack’s ‘Hellenization thesis.’ He writes:
One reason for James’s confusion about Luther might be traced to his dependence on the scholarship of the contemporary giant of German liberal Protestantism, Adolph von Harnack. Harnack, the eminent German Lutheran scholar of his times, proclaimed doctrine defunct: “The history of dogma comes to a close with Luther.” In seven probing volumes, Harnack argued the influential thesis that creedal dogma (such as Royce lifted up) is the historically contingent product of what he famously characterized as “the hellenization of the gospel.” Hellenization is understandable, Harnack explained; it was even inevitable. But this creedal theology formulated the gospel in the thought forms of Greek substance metaphysics; as such, these ideas are unintelligible to the modern mind and constitute an actual obstacle to faith. As indicated, Harnack argued that it was none other than Martin Luther who in principle if not yet to full effect overcame the intellectualizing and reifying theology of the old church. Luther recovered Jesus’ simple gospel of trust in the fatherly love of God. Couple this insight with the rise since Luther’s time of the modern scientific understanding of the world — which threatens to crush the human spirit with knowledge of its insignificance and impotence in the vast and ancient cosmos — and Jesus’ message of the fatherly God, rediscovered in principle by Luther’s idea of trust, fiducia, is surely the “essence of Christianity” and the gospel for our times. Theology as belief, theory, intellectual grasping of the divine with antiquated, reifying concepts like “nature” or “substance,” gives way to historically-critically founded preaching of existential trust in the world of Heraclitus.
Little in Harnack’s analysis has stood up to critical scrutiny. For example, Jaroslav Pelikan’s five-volume history of doctrine tells the countertale to Harnack of the evangelization of Hellenism: it is, he writes, a “distortion when the dogma formulated by the catholic tradition is described as ‘in its conception and development a work of the Greek spirit on the soil of the gospel’ [Harnack]. Indeed, in some ways it is more accurate to speak of dogma as the ‘dehellenization’ of the theology that had preceded it and to argue that ‘by its dogma the church threw up a wall against an alien metaphysic’” [Elert]. Step by painful step, Pelikan methodically dismantles Harnack’s construction of dogma as hellenization by means of a simple but crucial move: he takes dogma hermeneutically not theoretically, that is to say, as “what we believe, teach and confess on the basis of the Word of God” — an expression of the Lutheran Formulators which Pelikan borrowed to define the subject matter of his study. “Without setting rigid boundaries, we shall identify what is ‘believed’ as the form of Christian doctrine present in the modalities of devotion, spirituality, and worship; what is ‘taught’ as the content of the word of God extracted by exegesis from the witness of the Bible and communicated to the people of the church through proclamation, instruction and churchly theology; and what is ‘confessed’ as the testimony of the church both against false teaching from within and against attacks from without, articulated in polemics and apologetics, in creed and dogma.” When dogma is taken this way, as the complex act of the church’s interpretation of the gospel word of God in (continuing!) history, Harnack’s influential claim about Luther overcoming dogma turns out to be real sleight of hand.[1]
Ironically, I would contend, that even though Barth and Torrance, in particular, have been influenced heavily by Harnack’s thesis, they are not unself-critical. In other words, while seemingly in line with the mediating theologians in the modern, Barth and Torrance work into Pelikan’s thesis of ‘evangelizing metaphysics’; Torrance probably more than Barth, on this score.
What I still maintain, is that in the best of ecumenical creedal or conciliar theology we do indeed get what Pelikan counter-proposes vis-à-vis Harnack; we get metaphysics “evangelized.” But just like with ‘the Spirit and the flesh,’ there is an ongoing battle between sliding too much towards whatever the reifying philosophy might be. In other words: there are periods of theological development, I’d contend, where there has indeed been slippage back into an ontotheology of the sorts that Harnack was so concerned with. I think we see this in some of the substance metaphysics synthesized with Christian theology in the mediaeval period. But then we also get this slippage in the modern period with the synthesizing of Hegel, Kant et al. with Christian theology. It is the theologian’s burden to prayerfully translate and interpret the kerygma in their particular period in such a way that ‘evangelization’ is always at the fore. The reality is, is that it is inescapable for the theologian to transcend his or her periodized location, such that the reigning philosophies of the day won’t have impact on the way they attempt to articulate a theological grammar for their peers.
Maybe at the end of this I think Harnack, at least at his first impulses, had the right ‘spirit.’ But it is clear, at least to me (and others), that Harnack over-corrected; which is always the case in the organicism of the theological task. If anything, Harnack, alerts us to the real reality that the theologian can sublimate the Gospel to the spirit of the age rather than to the Spirit of the Christ; in this light, Harnack’s critique, ought to at least alert us all to be constantly vigilant in the way we attempt to think and speak God. Harnack, while overbaked, underscores our need to be prayerfully rigorous and in need of God’s discernment as we attempt to bear witness to the ongoing and living reality of the risen Christ with us.
[1] Paul R. Hinlicky, Luther and the Beloved Community (Grand Rapids, Michigan/Cambridge, U.K.: William B. Eerdmans Publishing Company, 2010), 26-7.