An intertextual focus with the prologue of 1 John on connections to the prologue of the Fourth Gospel has allowed Isaianic connections to be overlooked. The beginning of the letter in 1 John 1:1–3 echoes Isaiah 40:22. The Johannine reference to ‘what we have heard’ and what ‘we have declared to you’ gives the answer to the questions of Isaiah: “Have you not heard? Has it not been declared to you from the beginning?” The author asserts that they have heard, and they have announced the message to their audience.
The prologue of 1 John begins the rhetorical movement of the letter, and making the connection to Isaiah has at least two key rhetorical functions. First, it frames the message of which the author speaks as the fulfilment of Isaianic prophecy. In doing so, it provides encouragement for the audience in their context of division over Christology. By tying their position to Isaiah, they are reassured of being right, and that it is indeed their opponents who have departed from both them and the truth. Second, the use of Isaiah contributes to the authority of the author. By placing themselves in the role of one announcing God’s message, the author writes themselves into the story of prophetic fulfillment. The author takes on Isaiah’s mantle as one who speaks God’s words, adopting an authoritative role as one who conveys prophetic revelation.
However, when considering how Isaiah in turn draws on earlier texts, as what can be termed a ‘window reference’, a further function is evident. Isaiah’s question recalls the command of Deut 6:4–5 for Israel to hear. The Deuteronomistic call is a call to monolatry, a call that is expanded upon by Isaiah throughout chapter 40. For 1 John to take such a call to monolatry and repurpose it in a Christological context, it presents the message of Jesus as a revelation of the one true God of Israel. Thus for 1 John, the Isaianic echo also serves to assert the Johannine idea that the Son is the revealer of God the Father (John 1:18).