The Gospel and Biblical Theology
Graeme Goldsworthy summarizes the relationship and history between the two.
Because the gospel concerns the work of the historical Jesus Christ as the one who fulfils the OT promises, it is at the heart of biblical theology. When the plain meaning of the OT was lost to parts of the early church, often through the adoption of a dehistoricizing, allegorical interpretation of the Bible, the gospel ceased to be regarded as primarily what God has done in the historical Christ. The emphasis shifted to what God does inwardly in the human soul through piety and sacramental ministrations of the church. The Protestant reformers of the sixteenth century recovered the historical meaning of the OT and, with it, the historical gospel. A biblical theology which had its roots in the apostolic gospel was thus re-established.
Goldsworthy, “Gospel” in New Dictionary of Biblical Theology, p. 523
Nicely put. We can always count on Goldsworthy for some quality quotes!