Cardinal Jean Bilhere hired Michelangelo to make "the most beautiful work of marble in Rome."
Making comparisons is always tough but I can assure you that after seeing this sculpture, I don't think many sculptures can compete with its beauty.
It's one of main sights of St. Peter's Basilica and always surrounded by crowds and flashing cameras trying (unsuccessfully) to capture its perfect harmony and fragility. In photos, the look on Jesus's face, his passionate grimace, is reduced to nothing. The young Virgin seems to be the same age as her son. Here, the quest for beauty was Michelangelo's objective.