John’s prologue begins and ends with references to the wider narrative: the story he is about to tell has its origins ‘in the beginning’, and it is the crucial turning point in the continuing story of God’s dealings with the world which he has made. Within that wider narrative, God’s self-revelation to his people Israel is a vital factor; how, then, does the story the evangelist is about to tell relate to the Torah, and to the promises made to Israel? John’s answer is that Jesus Christ is the fulfilment of those promises because he is the fulfilment of the Torah itself – the true embodiment of God’s self-revelation which was glimpsed by Moses on Sinai [p. 188].
The relevance of John’s prologue to the rest of his Gospel is clear, but it nevertheless stands apart from it, and it is precisely because it stands apart from it that commentators have sometimes argued that it is a later addition to the Gospel [e.g. Robinson]. This over-analytic approach overlooks the purpose and necessity of a prologue for a narrative of this kind [cf. Barrett]. John’s prologue is no more an addition to the text than were the prologues to Shakespearian plays, which were intended to enable the audience to comprehend the plot. Once you know the story, of course, the need for a prologue is not so obvious [p. 189].
Morna D. Hooker, ‘Beginnings and Endings,’ in The Written Gospel, eds. Markus Bockmuehl and D.A. Hagner (FS Graham Stanton; Cambridge: CUP, 2005), 188-89.