There was among the theologians of [Lutheran orthodoxy] a deep awareness of man's - and this means also the theologian's - waywardness and sinfulness and congenital blindness, which pervades also the realm of the intellect...Correlative to this view of man was a recognition amongst the theologians of that period that the theologian in particular was in constant need of God's grace and of the Spirit's enlightenment, that the theologian to carry out his calling must depend on faith in Chirst and His Word and be a man of prayer. In other words, the personal experience of the Law and the Gospel in one's faith-life is the indispensable condition for all one's theologizing.
Robert Preus, The Theology of Post-Reformation Lutheranism (Concordia, St Louis/London, 1970), Volume 1, pp406-407.
Theologia est habitus practicus (theology is a practical aptitude) is an axiom of Lutheran theology. This means that theology is not simply a body of abstract truths, nor only the knowledge of these truths, but also the experience of these truths in life and the God-given ability to apply them to the Christian life (2 Corinthians 2:16ff, 2 Tim 3:16-17, Hebrews 5:14). Thus knowledge and faith, theology and piety, head and heart cannot separated.
Reflecting again on the "great theologians", a notable characteristic of them is that they were godly men; many of them (Augustine, Anselm, Aquinas, Luther, Gerhard) wrote profound hymns, prayers and devotional works as well as producing theology of the highest intellectual order (for some, prayer was itself the highest expression of theology). There was in them no separation between faith and life, knowledge and piety, head and heart.
This seems to me to be in contrast to the theologians of the modern period (with conspicuous exceptions). The post-Enlightenment period marks the beginning of a separation of theology from the life of the church, as theology is consigned to a "department" in the now increasingly secular universities (no longer the "queen of the sciences", but an increasingly despised hand-maiden). Theology welcomes the release from the constraints of confessional commitments and the freedom to seek open inquiry. The noetic effects of sin, even on the mind of the theologian liberated from confessions, become ever more apparent even as the reality of sin is denied.
Having given up solid ground on which theology once stood, the professional theologians should have been the last to be surprised when the role of theology departments in secular universities was relativised completely and they become mere centres for "religious studies". Confessional theology survives, by and large, only in the seminaries and church run colleges, where it can at least conserve the tradition relatively unmolested, but only at the expense of exile from the centres of intellectual life of the wider world. Few theologians manage to bridge the gap and obtain a hearing in both church and academy. The professionalisation of theology in the second half of the 20th century sees the Ph. D. become the "indispensable condition" for theologising, rather than "the experience of Law and Gospel in one's faith-life". Man, with his parchments and acclaim, now makes theologians, not God.