Isa 8:16 is considered a key reference regarding the formation of the book of Isaiah and the role of prophetic disciples in this process. This article argues, however, that originally this verse had a more limited significance. The instruction to which v. 16 refers is to be identified with vv. 12-15 rather than an early ‘book’ of Isaiah. The expression ‘the instructed ones’ (of YHWH rather than the prophet) is applied to the prophet’s audience. This term reflects Isaiah’s characteristic view of prophesying as an act of instruction and prophecy as a form of teaching, and it does not presuppose the existence of any prophetic school. The view that sealing the instruction would allude to preserving prophetic teaching for the posterity is discounted here in favour of understanding the symbolic act as a metaphor from the legal sphere refering to authentication, with no inherent temporal significance. More...