Isaiah confided his testimonies and
teachings to his disciples in order to guarantee the authenticity of the
predictions they contained after the failure of his first incursion into Judean
foreign affairs (Isa 8:16). This written copy is called a “testimony” (tē’ûdâ),
an indication that predictive prophecies could take on a quasilegal status when
written and notarized for purposes of authentication comparable to the
prophetic “witness” written in a “book” alluded to at Isa 30:8-11. (Joseph
Blenkinsopp, Opening the Sealed Book: Interpretations of the Book of Isaiah
in Late Antiquity [Grand Rapids, Mich.: Eerdmans, 2006], 6-7)