Requiem is the final mission of Hitman: Blood Money. At this point it is believed that Agent 47 is dead, after being poisoned by Diana Burnwood. Burnwood is present at the ceremony briefly, but departs after laying the Silverballers on 47's chest and giving him a quick kiss.
As what is presumed to be the final moments of 47's story play out, instead of observing the credits, you can trigger 47's resurrection by pressing forward movement button/analog multiple times, which will gradually fill 47's health bar. This ability to resurrect is the result of the antidote from Diana's kiss.
Once it's filled, a slow-motion moment - which lasts shortly - will be activated to allow 47 a period of time to take out a few enemies around him before it runs out. It's best to use this time to kill Alexander Leland Cayne and armed targets who are closest to 47's position, due to the fact that it can be difficult to find adequate cover. Killing Cayne will take a few double shots (for some reason, possibly a programming issue, a shot to the head won't kill him instantly), so you may want to use this time to get him out of the way early when he's unprepared. If you don't shoot him, fatally or otherwise, he will drive away when the shooting starts and go to the parked cars. If you choose to target the guards instead, Cayne will have to be dealt with later and quickly since his weapon is very powerful.
In the first part, because you have enemies almost everywhere, and there is no good cover for you immediately after 47 get up. Try to use someone as human shield to buy you some time.
Eliminating the Opposition
After being resurrected, the only objective is to clean house. Nobody, not even Rick Henderson or the priest, is to be left alive. There are several ways to make a stand against the opposition in this mission. Note that there is one special black NPC with cornrows who might throw a bomb at 47 if he enters cover and kill him instantly, so it's a good idea to take him out early. Thankfully, because all of the NPC are targets, you can use you map to find them even on Pro difficulty. Because the Silverballers' ammo tends to dry up quickly, you'll have to pick up guns from NPCs to survive. Most targets will be at the funeral, except for two guards on the outside who usually show up some time after the shooting starts, and the priest, who will walk up the hill until he sees 47 alive.
The death bed which 47 lies on originally can provide cover for a short while, but on higher difficulties, NPCs may decide to flank from any of the surrounding fields.
Similar to the death bed, the height of all the inner walls do not totally conceal your presence, and can leave you vulnerable. For this reason, it is not recommended unless you find yourself conceal by numerous enemies.
Making your way out of the windows and into the field can make it easier to put distance between your targets and dodge incoming gunfire.
After all other enemies are eliminated, kill Rick Henderson at the gate to the cemetery to wrap up this final mission.