What is doctrine and what is theology and why are they important? Theos is Greek for God so theology is the study of God and divine things. Doctrine is a teaching or belief from Scripture. John Frame writes, “The purpose of teaching is not merely to state the objective truth, but to bring the people to a state of spiritual health.” He defines theology as “the application of Scripture, by persons, to every area of life.” So we see that theology applies to every area of life.
All theology, all doctrine, is to be practical. That is, any truth rightly understood will move us to something. That is precisely what we see in Scripture; take the book of Ephesians for example. Paul laid out God’s amazing work in salvation: we were dead in our sins but God made us alive through Christ. After teaching on weighty truths for 3 chapters he then says “I therefore [because of the truth of the doctrines I have just shared] … urge you to walk in a manner worthy of the calling to which you have been called” (Eph. 4:1). He then proceeds from the doctrine to give application of that teaching for the remaining 3 chapters (for example he calls the Ephesians to unity in 4:1-6 and to sacrificial love in 5:1-2). If we are going to seek to live as the Lord has called us to live it is absolutely vital that we pray and seek to understand the incomprehensible love and glory of Christ (i.e. doctrine/theology; although, that does not mean that you will have to read theologies but it will at least include pouring over the Scripture).
F. F. Bruce has said,
“Doctrine is never taught in the Bible simply that it may be known; it is taught in order that it may be translated into practice: ‘if you know these things, blessed are you if you do them’ (Jn. 13:17). Hence Paul repeatedly follows up an exposition of doctrine with an ethical exhortation, the latter being linked to the former… often …with the particle ‘therefore’ (cf. Eph. 4:1; Col. 3:5).”
The scripture and its teachings are not senseless banter but truth that must be understood and lived out. And if we understand the truths rightly they will not be drudgery but rather delight. For instance, we know that we are to love others, but why? Because the Scripture teaches us that God loves us (doctrine) therefore we love others (application). First John 4:19 concurs, “We love because He first loved us.” Both the doctrine (understanding God’s love) and the application (loving others) are vital and should never be divided.
So, for example, if we want to give more money to missions we must first not merely give but understand why we give. If we want to do good things (at least effectively and God glorifyingly) it is important that we understand the grounds for what we do, for when doctrine comes before duty our duty is less duty and more delight. I am confident that Paul himself could not have endured all he did without his soul-satisfying doctrine. He endured persecution, but it was merely “a light momentary affliction” compared with the doctrine of heaven, a place where he knew he would receive unimaginable joy.
As Christians, our living is wrong if not influenced by doctrine, and our doctrine is wrong if it doesn’t influence our living. Both doctrine and living are to be inseparable; they are to complement and intensify each other. J.D. Payne has rightly said, “Orthodoxy (right belief) results in orthopraxy (right action); if not, then our orthodoxy is to be questioned.”
A deep understanding of doctrine, as well as an understanding of the God we serve, will, or should, reciprocate a radical living out of that doctrine; this is found throughout scripture. Doctrine in scripture is given for that very purpose: to change us. As J.I. Packer has said, “Theology is for doxology and devotion—that is, the praise of God and the practice of godliness.”
A prime example that comes to mind is found in Second Corinthians 8:9 where it talks about the radical impact the doctrine of the atonement had on the Macedonians. So beware, I am saying that the awesome truths of Scripture do not leave us unscathed. Rather, they call us to awesome, even drastic change; from darkness to light; from sons and daughters of Satan to sons and daughters of God; from being dead in Adam to being alive in Christ; from following Satan to being like Jesus who is God the Son.
 John M. Frame, The Doctrine of the Word of God (Philipsburg, NJ: P&R Publishing Company, 2010), 275.
 Ibid., 276. Italics his. “Teaching… is the use of God’s revelation to meet the spiritual needs of people, to promote godliness and spiritual health” (John Frame, The Doctrine of the Knowledge of God, 81).
 F.F. Bruce, The Epistle of Paul to the Romans: An Introduction and Commentary. The Tyndale New Testament Commentaries. (Grand Rapids, MI: Wm. B. Eerdmans Publishing Co., 2003), 212.
 J.D. Payne, Evangelism: A Biblical Guide to Today’s Questions (Colorado, CO: Biblica Publishing, 2011), XIII.
 J.I. Packer, Concise Theology: A Guide to Historic Christian Beliefs (Wheaton, ILL: Tyndale House Publishers, Inc, 1993), xii.