A pithy and useful definition of theology from the Catechism of the Lutheran David Chytraeus (1530-1600):
Quid est theologia seu Doctrina Christiana?
Theologia est doctrina de DEI essentia et voluntate ac beneficiis generi humano propter Christum meidatorem exhibitis, et cultibus ipsi vicissim debitis, patefacta in verbo Dei per Prophetas et Apostolos tradito, et illustribus testimoniis miraculorum confirmata, per quam DEUS vere efficax est, et veram sui agnitionem, remissionem peccatorum, et vitam aeternam credentibus impertit.
What is theology or Christian doctrine?
Theology is doctrine concerning the essence and will of God and his kindnesses shown to the human race on account of Christ the Mediator, and the worship owed to him in turn–[a doctrine] revealed in the Word of God that was handed down by the Prophets and Apostles and confirmed by the manifest testimonies of miracles, through which [doctrine] God is truly efficacious and imparts true knowledge of himself, the remission of sins, and eternal life to those who believe.1
