The scene begins with a long focal length establishing shot showing a crowd of people in a church surrounding a baptism. Extra-diegetic organ music overlays the scene.
Michael and his sister (holding her baby) walk up to the priest as he begins to speak. A close-up of Michael is shown followed by a close-up of the baby. These shots are short to condense time.
The next shot is not in the church–it is in a separate location, perhaps a motel room; it shows an assassin loading his AK47. This parallel montage is used throughout the scene to show that while the baptism is taking place, Michael’s men are assassinating the leaders of the “five families.”
Shots of five assassins (and their victims) in four separate locations are spliced with shots of the baptism.
The priest performing the baptism speaks in Latin whilst in the church, and his words are overlayed when the shot switches to the murders. His diegetic words become extra-diegetic via editing.
Another edit I would like to mention occurs for a split second at 4:10 and then again from 4:15-:16. The camera shows a man lock another man inside a revolving door. The man outside the revolving door holds a gun and begins shooting at the trapped man. As this happens, white bullet-hole cracks appear on the glass of the revolving door. At 4:10 and 4:15 the camera switches from the point of view of the shooter to the point of view of the victim; the shots alternate between being outside the revolving door and being inside the revolving door. This really caught my eye because when the camera switches to the view from inside the revolving door, it almost creates the effect that the viewer is being shot at, which is very disturbing.
Interestingly, no slow-mo or anything similar is used to expand the time of the gunshots. They happen rapidly and naturally. I think this lack of editing removes the viewer from the action; the viewer feels little to no emotional connection to the people being shot, which I think makes the shooting that much more disturbing because many human lives are taken away in such a short amount of time, and they are not even given much screen time. To be given such little screen time makes the shootings seem mundane or ordinary, which is quite disturbing indeed.