Charles Spurgeon apparently had a wonderful mind given to him by God for understanding and preaching the Word of God. The more I learn about him the more I believe he was so gifted fo rthe special ministry that he had. He had the gifted to remember what he read. It is said that he could recall what he read while preaching.
As a young child his toys were books. He learned to read them early and quickly. Eventually he could read six ordinary books at a sitting, and as many substantial volumes in a week. A retentive memory and a computer-like recall system provided grist for the mill of preparation for sermons, lectures, and books. Spurgeon's magazine The Sword and the Trowel often contained as many as fifty book reviews from his pen — sufficient proof of his capacity. References here
The more you read the more you are able to think about a subject.
I wonder how Spurgeon would have done in the computer age. He had nothing but his pen. He had his books to read. He read books, which are now out of print.
How he had the ability to speak to great crowds is beyond my understanding. Of course there are many who do this very thing today. Billy Graham to name one.
I guess what I am trying to say, Spurgeon had a method that he was able to use to present and prepare a sermon. Understanding that the Holy Spirit was the guide to his thinking. Of course we believe that God via the Holy Spirit gives us direction as to preparation of sermons.
This pfd site has 216 pages of 41 sermons by Spurgeon
Charles H. Spurgeon's Personal Library
Spurgeon's study at Westwood, his family home, contained more than 12,000 volumes. The majority of these were acquired by a donor who gave them to Curry Library at William Jewell College (near Kansas City). Books, furniture, and all were moved there, where they resided in a room that was a replica of Spurgeon's personal study until 2006.
Emmett O'Donnell of spurgeongems.org announces all 3,563 C. H. Spurgeon sermons are now on his website.