I just read (yet again) Piper's classic, The Supremacy of God in Preaching. I think this is a book that all preachers should read at least once a year. It should be on the bookshelf closest to the Bible and other study materials. It is in this work that Piper quotes Spurgeon by noting that GOd's call to the ministry of the Word (that is, to preach) "is an intense, all-absorbing desire for the work" (p.18).
The Supremacy of God in Preaching can be laid forth in a Trinitarian formula:
I. The Goal of Preaching: The Glory of God
II. The Ground of Preaching: The Cross of Christ
III. The Gift of Preaching: The Power of the Holy Spirit
Piper notes, "God the Father, God the Son, and God the Holy Spirit are the beginning, middle and end in the ministry of preaching. Written over all ministerial labor, especially preaching, stand the words of the apostle: "From Him and through Him and to Him are all things. To Him be glory forever" (Rom 11:36; Piper, p.19).
One final quote to sum up from the Scottish preacher of old, James Stewart. He said the aim of all genuine preaching is "to quicken the conscience by the holiness of God, to feed the mind with the truth of God, to purge the imagination by the beauty of God, to open the heart to the love of God, to devote the will to the purpose of God."
Piper then sums up this lengthy quote by simply saying, "God is the goal of preaching" (p.20).