Mr. Shandy, his brother Toby, and Dr. Slop continue their conversation while waiting for Obadiah to bring the doctor's medicine bag. During a lull in the conversation, Corporal Trim, a man who works for Toby, walks into the house.

As soon as Toby sees the corporal, he asks the man to run over to his house and pick up his book by Stevinus, an engineer. The book is what had inspired Toby's conversation about war fortifications. Readers can assume that Toby wanted to continue that part of the discourse, possibly drawing references from the Stevinus book.

When Corporal Trim returns, Mr. Shandy asks him to go through the book to see if he can find a reference to a sail boat that Stevinus is accredited for engineering, as the previous conversation among the three men had involved this fact.

As the corporal searches through the book, a piece of paper falls out of the book. When Trim inspects the paper, he claims that there is something written on it. The writing begins with a quote from the Bible and so Trim concludes that it must be a sermon. Although Toby cannot imagine how a sermon was placed inside his Stevinus book, he asks Trim to read it.

Upon declaring that Trim is very competent in reading, a statement Trim reinforces, Toby informs his brother and the doctor that he considered Trim a scholar when both men served in the military together. Upon hearing this, Mr. Shandy asks the doctor if he minds listening to the sermon. Then the men settle back as Trim stands in the center of the room and prepares to read.

Before Trim begins reading, the narrator again interrupts the story to describe how Trim looks. The narrator claims that if he leaves these facts to the reader's imagination, Trim would probably be described as a soldier standing at attention. However, this is far from the truth. Trim's body is relaxed. He is standing at a slight angle, leaning forward, one foot placed a few inches in front of the other. This is the orator's stance, the narrator states, although the narrator does not know how Trim knows that he should stand in this fashion.

Trim does not read many words from the sermon before Mr. Shandy interrupts him. Shandy criticizes the way Trim is reading, suggesting that the tone of voice he is using is prejudiced against Protestants.

There ensues a conversation between Mr. Shandy and Doctor Slop concerning the differences between the Catholic religion and a generic Protestant religion. This discussion eventually is extended into the sermon that Trim is reading.

The topic of the sermon is the quality of a man's conscience. In the Catholic religion, the author of the sermon declares that a man does not have to have a conscience because the Church dictates what is right or wrong. Should a Catholic commit a crime, he need only go to confession to be forgiven. Protestants, on the other hand, have developed consciences for themselves, which tell them when they do something wrong.