How Systematic Theology Works

Because [systematic theology] aims to synthesize all of Scripture and to interact with the broadest questions, the categories it uses must transcend the usage of individual biblical books or writers. For instance, systematicians speak of the doctrine of justification, knowing full well that the justification word-group does not function exactly the same way in Matthew as it does in Paul; they speak of the doctrine of the call of God, where exactly the same observation about "call" language must be made.

--D.A. Carson and Timothy Keller, "Gospel-Centered Ministry," in The Gospel as Center: Renewing Our Faith and Reforming Our Ministry Practices (edited by D.A. Carson and Timothy Keller; Wheaton, IL: Crossway, 2012), 19.