I have only just realized that Zondervan has put up an excerpt from Evangelical Theology on-line featuring the introduction and the first two chapters about prolegomena.
A good summary of what I say is:
If prolegomena is concerned with orientating ourselves to the theological task and setting forth the divine revelation, then the primary function of an evangelical prolegomena should be a setting out of the gospel. The gospel explains why we are in the theological race in the first place, and the gospel is the nexus into the reality of the God who has revealed himself … To set forth the gospel in our prolegomena is to establish the beginning, center, and boundary of evangelical theology. An evangelical theology begins with the gospel because the gospel establishes the hermeneutical horizons for its talk about God and constitutes the purpose or raison d’être of the church’s existence … The gospel is the driving force behind doctrine and its actualization within the Christian community. Theology has its agenda and energy derived from the good news of Jesus Christ. It is, dare I say, the beauty of the gospel that matures our theological reflection on who God is toward us in Jesus Christ.
Well, that is what the book is about!