In Preaching & Preachers, Martin Lloyd-Jones contends that preaching must always be theological:
To me there is nothing more important in a preacher than that he should have a systematic theology, that he should know it and be well grounded in it. This systematic theology, this body of truth which is derived from the Scripture, should always be present as a background and as a controlling influence in his preaching. Each message, which arises out of a particular text or statement of the Scripture, must always be a part or an aspect of this total body of truth. (77)
Lloyd-Jones goes on to describe the essence of preaching as theology on fire:
What is preaching? Logic on fire! Eloquent reason! Are these contradictions? Of course they are not. Reason concerning this Truth ought to be mightily eloquent, as you see it in the case of the Apostle Paul and others. It is theology on fire. And a theology which does not take fire, I maintain, is a defective theology; or at least the man’s understanding of it is defective. Preaching is theology coming through a man who is on fire. A true understanding and experience of the Truth must lead to this. I say again that a man who can speak about these things dispassionately has no right whatsoever to be in a pulpit; and should never be allowed to enter one.
What is the chief end of preaching? I like to think it is this. It is to give men and women a sense of God and His presence. … I can forgive the preacher almost anything if he gives me a sense of God, if he gives me something for my soul, if he gives me the sense that, though he is inadequate himself, he is handling something which is very great and very glorious, if he gives me some dim glimpse of the majesty and the glory of God, the love of Christ my Saviour, and the magnificence of the Gospel. If he does that I am his debtor, and I am profoundly grateful to him. Preaching is the most amazing, and the most thrilling activity that one can ever be engaged in, because of all that it holds out for all of us in the present, and because of the glorious endless possibilities in an eternal future. (110-111)
Preaching is theology coming through a man who is on fire.
Lloyd-Jones reiterates that “preaching means delivering the message of God” and that this involves “the relationship between systematic theology and the exact meaning of a particular text.” Topical talks, divorced from healthy hermeneutics and robust theology, lack the power of the Word rightly divided. When preachers expound the texts of Scripture within the framework of their systematic theology, and exult over the truths at hand, hearers will enjoy a sense of God.