The following is an assignment from one of my classes... we were to define theology and then we had a discussion on whether theology could be sinful.
Theology is the study of God (Father, Son, and Holy Spirit) in and through his self-revelation, human religious experience (including church practices like worship and teaching, and the processes of salvation, sanctification, and glorification), faith, spirituality, and orthodox church tradition, resulting in the pursuit of (and conformity to) Truth as expressed in Scripture – all of which being ultimately for the glory of God. Systematic Theology seeks to express in a cogent, coherent system of beliefs the commands, teachings, principles, implications, truths, and spirit of the Scriptures in addition to the God with whom they are concerned and from whom they come.
It seems to me that theology can and does become sinful when it begins to be an end in and of itself. When a theological perspective ceases being first and foremost for the glory of God in Christ Jesus, and becomes more dedicated to proving itself (its logical consistency, its universal appeal, its biblical basis, etc.), replicating itself, or making itself known and respected rather than aiding discipleship of the saints in understanding God’s self-revelation, it has dethroned God (by making him and his glory a secondary or tertiary goal) from his rightful place and has exalted itself above him. In this way, it becomes sinful.
For example, if I quote a certain theologian (Augustine, Calvin, Luther, Edwards, Grudem, Piper, Driscoll) – or any other man, for that matter – more than I quote Scripture, and if I know a certain book or collection of writings better than I know the Scriptures themselves then I have begun traveling down this road. Rectifying this situation does not involve merely reading the Bible more and studying it more intently… rather, it begins with repentance for idolatry, turning from my trust of fallible humans over the infinite God and pursuing what he has said above all others.
This is not to say that theologians are detrimental or obstruct our understanding of the Scriptures. The men mentioned above have been immensely formative to my beliefs and my sanctification. The sin lies not with the theologian (unless they are a heretical false teacher), but rather with me. If I put my trust in Grudem’s theology or Edwards’ sermons or Calvin’s doctrine before I put my trust in the Scriptures from which they are derived, then I have turned the appropriate order on its head – I have begun examining the Scriptures through a theologian’s lens rather than measuring a theologian’s claims against the Scriptures.
The end goal of theology, then (as far as I can tell), is the study of God’s self-revelation in such a way as to bring him glory through truth-based spirit-filled worship, bold Christ-centered gospel-saturated preaching and teaching, and through the transformed lives of Christ followers working out the lifelong process of sanctification.