why was Manny so important?

The director wants to explain that in matters of Heaven, every single person is important no matter what they are or do, even if that person is a simple boxer, he just explains that each person plays an important role in the destiny of world and gives a new meaning to life. This time was Manny next time it could be you. Funny how the destiny of the entire human race can depend on a truck driver, a flight attendant, a receptionist or a retired boxer.