The following excerpt is from William Burt Pope’s Compendium of Christian Theology (2nd edition).
Christian Theology is the science of God and Divine things, based upon the revelation made to mankind in Jesus Christ, and variously systematised within the Christian Church.
All that belongs to the preliminaries of our study may be distributed under the several heads suggested by this definition, which is so framed as to include, first, Theology proper; secondly, its limitation to the relations between God and mankind; thirdly, its essential connection with Christ; fourthly, its characteristics as developed under various influences within the Christian Church; and lastly, its title to the name of a science. The introductory remarks which will be made on these several topics have for their object simply to prepare the mind of the student for what lies before him; and to give a few hints which will all afterwards be expanded in due course.
God is the source and the subject and the end of theology. The stricter and earlier use of the word limited it to the doctrine of the Triune God and His attributes. But in modern usage it includes the whole compass of the science of Religion, or the relations of all things to God. This gives it its unity and dignity and sanctity. It is a Deo, de Deo, in Deum: from God in its origin, concerning God in its substance, and it leads to God in all its issues; His Name is in it.
1. The only adequate definition of this subject embraces Divine things: λόγος περὶ τοῦ Θεοῦ καὶ περὶ τῶν θείων. The Supreme, whose Being is the first postulate of theology or divinity, declares Himself to be as to His nature incomprehensible and unsearchable. I am that I am (Ex. 3:14) is the nearest approach to a definition; it asserts without proving His existence, and that He exists in an essence known only to Himself. The Old Testament asks: Canst thou by searching find out God? canst thou find out the Almighty unto perfection? (Job 11:7) The New Testament, which brings Him nearer in His Son, represents Him as dwelling in the light which no man can approach unto (1 Tim 6:16) to search. In the profoundest sense He is ever the Unknown God. (Acts 17:23) It is His glory that He must conceal Himself. But St. Paul, as a preacher to the Gentiles, nevertheless declares that Unknown God, and in his writings uses two expressive phrases which at once affirm the prerogative and assign the limits of our theology proper. He speaks of the things of God, (1 Cor. 2:11) τὰ τοῦ Θεοῦ, in reference to those mysteries which the Spirit can and will reveal to those who receive Him. And he indicates that even apart from the supernatural revelations of the Spirit that which may be known of God, (Rom. 1:19) τὸ γνώστον τοῦ Θεοῦ, is unfolded to man. All that is known is all that may be known: the possible knowledge is the actual knowledge in its successive communications from the light of nature to the light of grace and thence to the light of glory. The thick darkness round about the unsearchable Presence is not absolutely unbroken: the rays that flow from it penetrate every department of true knowledge, especially of this.
2. There is a sense in which universal theology is concerned simply with the relation of all things to God: if we carefully guard our meaning we may make this proposition include the converse, the relation of God to all things. Relation of course must be mutual; but it is hard in this matter to detach from the notion of relation that of dependence. The Eternal One is the Unconditioned Being. When we study His nature and perfections and works we must always remember that He is His Perfect Self independent of every created object, and independent of every thought concerning Him. But there is not a doctrine, nor is there a branch or development of any doctrine, which is not purely the expression of some relation of His creatures to the Supreme First Cause.
3. Hence every branch of this science is sacred. It is a temple which is filled with the presence of God. From its hidden sanctuary, into which no high priest taken from among men can enter, issues a light which leaves no part dark save where it is dark with excess of glory. Therefore all fit students are worshippers as well as students. In the heathen world there was a true instinct of this. The highest tribute the ancients could pay to their poets and philosophers, from Homer and Hesiod downwards, was to call them θεολόγοι. Their philosophy was their theology. So in the early Church, when theology put on its perfection, its relation to God was the seal of that perfection: St. John was called the Divine, ὁ θεολόγος, because his writings contained most of the manifestation of the Holy Trinity in its internal and external relations. What has been said of God Himself may be said concerning the theological study of God: He is the centre everywhere of a science which has its circumference nowhere. The remembrance of this must exert its influence upon our spirit and temper in all our studies. Who shall ascend into the hill of the Lord? or who shall stand in His holy place? He that hath clean hands, and a pure heart. (Ps. 24:3, 4)