Systematic theology is not itself revelation. Dogmatic theology developed as the church reflected on the manifold revelation of God in Scripture. The motivation for this task was an attempt to systematically apply the teaching of the Bible to the thinking and conduct of the people of God. Individual theologians like Athanasius, Augustine and Calvin exerted huge influence on the development of Christian dogma. But the church's growing understanding of the revelation of God is above all, a result of the work of the Holy Spirit.
"[The Spirit] has been present in the church in all generations of the church's history, endowing the church in its organic unity as the body of Christ with gifts of understanding and expression. It is this ceaseless activity of the Holy Spirit development throughout the centuries of what we call Christian doctrine. Individual theologians are but the spokesmen of this accumulated understanding which the Spirit of truth has been granting to the church. Christ as Head of the church must not be thought of apart from the Spirit nor the Spirit apart from Christ". (p. 6)
This does not mean progress in understanding has been uniform. There have been decadent periods of church history when vital truths were overlooked and neglected. In those times, there was little in the way of advance. But there have also been periods of epochal contribution to the church's theological task. Heresy has often had the effect of forcing the church to look afresh at Biblical doctrine and to state her understanding of that teaching with greater force and clarity. The Arian controversy of the fourth century is a case in point. In the light of that disputation, the church declared that the Son is homoousion (same essence) with the Father. In doing so, the church safeguarded her witness to the full deity of Christ. As Murray puts it,
"The church's confession had been in the balance but the Head of the church guarded the interests of his honour." (p. 7)
For Murray, the Reformation was the golden age of creedal precision and formulation. He has Calvin's Institutes of the Christian Religion particularly in mind. The Protestant teaching of that period built on the earlier creeds of the church and expressed with great clarity the Biblical teaching on salvation. Murray's writings on John Calvin and the Westminster Confession of Faith bear eloquent testimony to his esteem for the theological wisdom of the Reformation and Puritan periods. (See Collected Writings 4: Studies in Theology for Murray's work in historical theology).
Systematic theology must be contemporary, but not at the expense of the dogmatic advances of the past. Turning our backs upon the great doctrinal achievements of the church in order to reinvent the the theological wheel in every generation,
"dishonours the Holy Spirit by whose endowments and grace epochal strides in understanding and precision have been taken." (p. 7)
Murray's emphasis on the value of historical and creedal theology is welcome. He gives due recognition to the role of the Holy Spirit in leading the church to understand the revelation of God in Scripture. The theological traditions of the church encapsulated in the historic creeds and confessions help the people of God in all generations to understand and apply the Biblical teaching. At a time when creedal statements are often regarded as outmoded, we need to be reminded that the theological task is no momentary, individualistic affair. We need all the wisdom and insight of the people of God in past generations to enable us to grasp the riches of the gospel. This is part and parcel of the communion of the saints. But tradition is not to be elevated to the level of Scripture. Our theology must always be open to revision in the light of God's Word.
John Murray's account of the relationship between systematic and historical theology avoids the nihilism of the anti-traditional stance of fundamentalism. Also, in clearly distinguishing between Biblical revelation and dogmatics, he refuses to accord magisterial authority to tradition. For Protestants there can be no Roman Catholic style Magesterium that stands alongside or suppliments Scripture.
Kevin Vanhoozer puts this in typically theodramatic terms,
"The Spirit thus brings about a mutual indwelling of canonical script and performing community, incorporating us not only into the drama of redemption but into the actor who stands at its very heart. As a work of the Spirit, tradition plays the role of the moon to the Scripture's sun: what light, and authority, tradition bears, it does so by virtue of reflecting the light of the Son that shines forth from the canon." (The Drama of Doctrine, WJK, 2005, p. 210)
Page references are to Collected Writings of John Murray Volume 4: Studies in Theology, Banner of Truth Trust, 1982.