I have tried this method. I have also ran pink noise and set the graph with the EQ for a flat setting. Then, when you stand at the pulpit and talk, the sound can be muddy or just awful. Part of the difficulty with either method is the room. It is a fact that most churches have acoustical problems.
Some problems are on the stage, other problems are in the seating area as well.
When placing the test mic in the audience area, the room can change the response greatly when you move the mic only a few feet away. Point the microphone straight back to where a person would be standing to give a sermon or back wall. Pointing the mic the other way doesn't work very well. With a Dynamic mic, it is more forgiving when EQ'ing such as the old Shure SM58. It is best to use a tripod base mic stand.