Isaiah 28 closes with a parable.  Like New Testament parables, one key to interpreting them is to note repetition (in this case the idea of being taught by God in vv. 26 and 29).  The successful farmers believe in God’s ways and farm their land accordingly, unlike God’s people.  Isaiah was addressing God’s people, many of whom, were not trusting and obeying God.  That’s the point of this section: God’s people are encouraged to believe and obey God’s word like the farmers in the parable do.  Verse 29’s description of our Lord is designed to drive us to depend on Him for guidance and direction through life.  Remember that Isaiah is continuing to urge God’s people to stop the trend of looking more and more like society and less and less like their Savior.  Meaning for parables are often disclosed through the law of end stress (what comes last is important).  This certainly is true in 28:29.  We shouldn’t forget at Christmas time that this description of God first occurred back in Isaiah 9:6 where it points to our Savior, the Son given to us.