Why is it canonical?

In the later years of his career, Michelangelo enjoyed both the reputation of an artist that epitomized the previous generation, and the opportunities to work on some of the most important commissions in all of Europe of the age. This altarpiece, a fresco on a wall in the same chapel where he painted his famous ceiling, is deep with biblical imagery and is perhaps one of the most important works created by Michelangelo in his entire career.