Theology is the science of God and of the relations between God and the creation. The word "theology" is commonly used to describe a more theoretical displine looking at the existence and sovereignty of God, creation, and other similar topics, drawing from philosophy and a variety of other disciplines. Theology is the science of the sciences because it reveals the underlying ground which all other sciences require for their complete explanation.
Christian theology is the application of Scripture by believers to all aspects of life.1 Theology has to do with the good, the truth, and the beautiful. It involves the whole of the believer: the head, the heart, and the hands (what we think, how we feel, and what we do). It's goal is to allow us to know and serve God, to meet the spiritual needs of his people and the world, and to promote godliness. It relies on the Bible first and foremost as the infallible word of God, but it also uses insights from other disciplines.
"Every Scripture is God-breathed and profitable for teaching, for reproof, for correction, and for instruction in righteousness, that each person who belongs to God may be complete, thoroughly equipped for every good work." (2 Tim 3:16-17).
"Therefore leaving the teaching of the first principles of Christ, let’s press on to perfection—not laying again a foundation of repentance from dead works, of faith toward God, of the teaching of baptisms, of laying on of hands, of resurrection of the dead, and of eternal judgment. This will we do, if God permits." (Heb 6:1-3).
"The secret things belong to Yahweh our God; but the things that are revealed belong to us and to our children forever, that we may do all the words of this law." (Deut 29:29).
"Always be ready to give an answer to everyone who asks you a reason concerning the hope that is in you, with humility and fear, having a good conscience. Thus, while you are spoken against as evildoers, they may be disappointed who curse your good way of life in Christ." (1 Pet 3:15-16).
"Remind them of these things, charging them in the sight of the Lord that they don’t argue about words to no profit, to the subverting of those who hear. Give diligence to present yourself approved by God, a workman who doesn’t need to be ashamed, properly handling the Word of Truth. But shun empty chatter, for it will go further in ungodliness, and those words will consume like gangrene, of whom is Hymenaeus and Philetus: men who have erred concerning the truth, saying that the resurrection is already past, and overthrowing the faith of some. However, God’s firm foundation stands, having this seal: 'The Lord knows those who are his,' and, 'Let every one who names the name of the Lord depart from unrighteousness.'" (2 Tim 2:14-19).
1. This definition of theology and the perspectival notion of theology is based on the work of John Frame in Systematic Theology: An Introduction to Christian Belief (Phillipsburg, NJ: P&R, 2013), Ch. 1. John Frame is “seeking to discourage the notion that theology is 'properly' something theoretical, something academic, as opposed to the practical teaching that goes on in preaching, counselling, and Christian friendship,” The Doctrine of the Knowledge of God (Phillipsburg, NJ: P&R, 1987), pp. 81-85.