There is a kind of sermon which piles on cross references and parallel texts and is stuffed with scriptural words and yet is uninteresting – which seems odd. The trouble is that merely collating Scripture with occasional remarks is not how Scripture works.

Consider an example: one likes Shakespeare: then shouldn’t I like a random series of quotes? Why does it not give the same pleasure as the play itself? Because it is not the same thing- it as an artificial construct made from the original words.

James W. Alexander speaks to this issue as follows:

Another method which I pursued, was to choose a text, and then having written out in full all the parallel passages, to classify them, and found my divisions on this classification. Then to connect all these passages, interweaving them with my own remarks. 

I flattered myself that this was a happy method, because it made my sermon scriptural. It did so indeed, but it had great disadvantages.

 The nexus between the texts was factitious; often refined and recondite; and always more obvious to the writer than it could be to the reader. It prevented the flow of thought in a natural channel. 

It was like a number of lakes connected by artificial canals, as compared with-a flowing natural stream. The discourse was disjointed, and overladen with texts, and uninteresting. 

I am convinced that those passages of Scripture which suggest themselves unsought, in rapid writing or speaking, are the most effective; nay, that one such is worth a hundred lugged in.

To be Scriptural in preaching, we must be familiar with the Bible at common times. Hence one of the great advantages of preaching without notes, even in regard to method. Such is the sympathy between soul and soul that a connection of thoughts which is easy, agreeable, and awakening to the hearer, will always be found to be that which has been natural and unconstrained in the mind of the preacher. 

The best way is, to study the parallel places exegetically, perhaps as they lie in the Scripture, and then to let them come in or not, as they may suggest themselves during preparation.”

JAMES W. ALEXANDER, D.D. “THOUGHTS ON PREACHING BEING CONTRIBUTIONS TO HOMILECTICS.” iBooks.