Without any hesitation, I always count the Old Testament (Hebrew Scriptures) Book of of the prophet Isaiah as one of my all-time favorite portions of the Bible.  The Lord used this prophet to declare not only the sin of God's people in Israel, but also the cure for sin: God's own grace through a mighty Messiah (Anointed One) who was to come.

God does not hold back from exposing sin for all that it is in Isaiah.  Judgments are also spelled out and promised as an inevitable result of the sins of the people.  But greater than all of these is the grace of God and the incomparable promises of salvation and restoration by God's own Servant.  No other book speaks more clearly of Christ than the ancient prophet of Isaiah. 

If you want to know the heart of God for us all, then read and become totally familiar with the Book of Isaiah.  If you want to know why Jesus went through many of the things He did, then read and get to know thoroughly the writings of Isaiah.

Unbelieving "scholars" (but not true students of Scripture) have tried many ways to rid themselves of the power of God's Word in Isaiah.  This is nothing new.  The prophet himself faced many critics and enemies of the truth in his own day (see, for example, Isaiah 30: 8-13).  And tradition has it that he was murdered because of his testimony, his body sawn in half.  Likewise, modern critics still try to divide up the book of Isaiah, claiming that it could not have all been written by the same man.

Nevertheless, God has spoken and does speak.  The prophet Isaiah tells us so many things about Christ that one nickname for the book is the "Gospel of Isaiah."  Yet no critic has yet been foolish enough to claim that the book of Isaiah (or portions thereof) were written after Jesus died on the cross at Calvary.  (But give them time.)  In the mean time, we who know the Lord thank God for His work of grace in the prophetic words of Isaiah.