By In his Preface to Essential Truths of the Christian Faith, R.C. Sproul makes the following statement:
Every Christian is a theologian. We are always engaged in the activity of learning about the things of God. We are not all theologians in the professional or academic sense, but theologians we are, for better or for worse. The “for worse” is no small matter. Second Peter warns that heresies are destructive to the people of God and are blasphemies committed against God. They are destructive because theology touches every dimension of our lives.
The Bible declares that as a man thinks in his heart, so is he. This declaration sounds strange. It is almost as if the biblical writer blunders. He seems to confuse the mind and the heart. We normally associate thought with the brain and feelings with the heart. So what does it mean to say a man thinks in his heart? The phrase ‘to think in the heart’ refers to thoughtful reflection. Many ideas are briefly entertained by the mind without ever penetrating the heart. Those ideas that do grasp us in our innermost parts, however, are the ideas that shape our lives. We are what we think. When our thoughts are corrupted, our lives follow suit.
We all know that people can recite the creeds flawlessly and make A’s in theology courses while living godless lives. We can affirm a sound theology and live an unsound life. Sound theology is not enough to live a godly life. But it is still a requisite for godly living. How can we do the truth without first understanding what the truth is?
No Christian can avoid theology. Every Christian has a theology. The issue, then, is not, do we want to have a theology? That’s a given. The real issue is, do we have a sound theology? Do we embrace true or false doctrine?”