The minister does not appear in "A Rose for Emily" until near the story's end. When some of the townspeople disagree with her association and relationship with Homer Barron, they make a last-ditch effort to discourage her from seeing Homer by sending the minister to her house. In Part 4 of the story, Faulkner writes,
"The men did not want to interfere [in the Homer Barron situation], but at last the ladies forced the Baptist minister--Miss Emily's people were Episcopal-- to call upon her. He would never divulge what happened during that interview, but he refused to go back again."
This section of the story is ambiguous for several reasons. Faulkner includes Miss Emily's church affiliation but does not go further with that information. It could be that he includes the phrase to demonstrate how little the townspeople really know or truly care about Miss Emily. Next, Faulkner implies that something horrid or shocking happens while he visits, but then never explains what causes the minister to refuse going back. He simply writes that the minister's wife writes to Miss Emily's relatives.
One point of interest is that the minister makes his visit after Miss Emily has already purchased the rat poison. At this point, she might have hinted to the minister what she was planning; nonetheless, it's unclear. Regardless, the minor event in the story simply adds to the characterization of Miss Emily as rigid and traditional.
there are a couple of errors with the previous answer I would just like to clarify.
Firstly, The minister does visit Emily because the townspeople are concerned but not because her relatives disagree with her relationship, rather, they did not know anything that was going on until after the minister goes to her house and then contacts her cousins.
Another, more important error is that Miss Emily could not have already murdered Homer Barron by the time the minister visited, because after he left, he contacted her cousins, and during her cousins' visit, Homer leaves for a while (that is when she purchases the arsenic, not before the minister visits). The story says that after her cousins go home, Homer comes back and is last seen entering Miss Emily's house. And that is when she poisons him.