Immediate and Mediate
The distinction between Scripture as immediate and preaching as mediate word of God reflects the general Reformed tendency to view preaching as derivative, that is, as a result of the presence of God’s Word in the church.
Richard A. Muller, Post-Reformation Reformed Dogmatics: The Rise and Development of Reformed Orthodoxy; Volume 2: The Cognitive Foundation of Theology, 2nd ed. (Grand Rapids, MI: Baker Academic, 2003), 204.