CLAIM: Isaiah 8:16 states: “Bind up the testimony, seal the law among my disciples.” Critics argue that Isaiah believed that his disciples would finish his work, which is sometimes referred to as “Second” Isaiah. Is this the case?
RESPONSE: This view terribly misinterprets this passage. Isaiah did not write that his book would be finished his disciples (hundreds of years in the future). Instead, he wrote that the testimony would be sealed among his disciples (c.f. Isa. 29:11; Jer. 32:14). Motyer writes,
‘Bind’ means to ‘wrap up’, to safeguard from tampering and ‘seal’ means to attest as final and therefore guard from addition. The imperatives suggest a definite act, a precise (even legal) securing of Isaiah’s message against any accusation that he did not say this or that and against subsequent tampering or addition by others.
For a full defense of the unity of authorship in Isaiah, see comments on the Authorship of Isaiah.
 Motyer, J. A. The prophecy of Isaiah: An introduction & commentary. Downers Grove, IL: InterVarsity Press. 1996. Isaiah 8:16.