"the instrumentality of philosophy in introducing these dogmas into the Christian religion, is no sufficient ground for asserting that they were foreign to Christianity and had nothing to do with it. It is a matter of perfect indifference where a thing originated; the only question is: 'Is it true in and for itself?' Many think that by pronouncing the doctrine to be Neo-Platonic, they have ipso facto banished it from Christianity. Whether a Christian doctrine stands exactly thus or thus in the Bible, the point to which the exegetical scholars of modern times devote all their attention, is not the only question. The letter kills, the spirit makes alive: this they say themselves, yet pervert the sentiment by taking the understanding [(Verstand)] for the spirit [(Geist)]. It was the Church that recognized and established the doctrines in question, i.e., the spirit of the Church; and it is itself an article of doctrine: 'I believe in a Holy Church'; as Christ himself also said: 'The Spirit will guide you into all truth.' In the Nicene Council (A.D. 325), was ultimately established a fixed confession of faith, to which we still adhere: this confession had not, indeed, a speculative form, but the profoundly speculative is most intimately inwoven with the manifestation of Christ himself. Even in John (ἐν ἀρχῇ ἦν ὁ λόγος καὶ ὁ λόγος ἦν πρὸς τὸν θεόν, καὶ θεὸς ἦν ὁ λόγος) we see the commencement of a profounder comprehension. The profoundest thought is connected with the personality of Christ, with the historical and external; and it is the very grandeur of the Christian religion that, with all this profundity, it is easy of comprehension by our consciousness in its outward aspect, while, at the same time, it summons us to penetrate deeper. It is thus adapted to every grade of culture, and yet satisfies the highest requirements."
Georg Wilhelm Friedrich Hegel, [Lectures on] The philosophy of history III.iii.2 ("Christianity"), trans. J. Sibree; GBWW,1st ed. (1952), vol. 46, p. 309. For the underlying German, see the (second?) Karl Hegel manuscript edition of 1840, p. 402.
It's what he means by Geist that can seem so frustratingly problematic!