It is sometimes contended that ministers need not be trained in systematic theology if only they know their Bibles. But “Bible-trained” instead of systematically trained preachers frequently preach error. They may mean ever so well and be ever so true to the gospel on certain points; nevertheless, they often preach error. There are many “orthodox” preachers today whose study of Scripture has been so limited to what it says about soteriology that they could not protect the fold of God against heresies on the person of Christ. Ofttimes they themselves even entertain definitely heretical notions on the person of Christ, though perfectly unaware of the fact.
If we carry this idea one step further, we note that a study of systematic theology will help men to preach theologically. It will help to make men proclaim the whole counsel of God. Many ministers never touch the greater part of the wealth of the revelation of God to man contained in Scripture. But systematics helps ministers to preach the whole counsel of God, and thus to make God central in their work.
The history of the church bears out the claim that God-centered preaching is most valuable to the church of Christ. When the ministry has most truly proclaimed the whole counsel of God, the church has flourished spiritually. Then, too, it is well-rounded preaching of this sort that has kept the church from worldliness. On the other hand, it has kept the church from an unhealthy other-worldliness. Well-rounded preaching teaches us to use the things of this world because they are the gifts of God, and it teaches us to possess them as not possessing them, inasmuch as they must be used in subordination to the one supreme purpose of man’s existence, namely the glory of God.
– Cornelius Van Til, An Introduction to Systematic Theology: Prolegomena and the Doctrines of Revelation, Scripture, and God, ed. William Edgar, 2nd ed. (Phillipsburg, NJ: P&R, 2007), 22–23.