One does not learn to speak or write prophetically.  It is not merely a genre of literature to be studied.  It is not dogma to be memorized, or a set of laws to be obeyed.  It is not even, contra modern critics, a feat of artistic imagination or poetry.  Rather, this manner of speech or writing is birthed in a person by the action of God Himself.  You cannot separate the revelation from the message:  Moses was made who he was by his meeting with God at the burning bush, Israel became the people of God at Sinai when God descended on the mountain with fire and smoke, and Isaiah became the prophet of God when he "saw the Lord seated on a throne, high and exalted" (Isa 6:1-8).  There were seraphim, an altar, a burning coal, and a Voice that proclaimed his sins were forgiven.  This encounter is the key to the man, and to the book he wrote.

       

At this time there was a “coming upon” Isaiah of the Spirit of God expressed through prophetic speech.  We have seen this action of God previously in the Book of Judges, when God's Spirit came upon a man or woman and filled them with power for a task or to be a judge over Israel.  We also saw it in 1 Samuel, when the earliest kings of Israel were similarly anointed and empowered to rule.  And so with Isaiah, but his anointing was not to be a judge or ruler, but to be the spokesman of God and the intercessor for his people.  And whenever the Spirit stirred in him afterwards, he would flow forth in impassioned words that came from that exalted throne, the same throne he had seen with his own eyes.  Prophetic speech is in essence the voice of the Spirit of God.