This marble statue is 2.16 meters tall and was commissioned in 1503 by the Opera del Duomo di Firenze, or the Cathedral Works Museum: the assignment included the creation of over-sized statues of the twelve apostles for the pillars under Brunelleschi's dome. The artist took on too much work and was forced to give up the project, and the only thing that remains is in fact the statue of St. Matthew.
Keep in mind that the statue was intended to be placed in a rather deep niche, and so it was made to be seen only from the front, and not from below as is usually the case. The saint's body looks like it's twisting, as if driven by an extraordinary internal force that seems to drag it upwards. A step at the lower left of the sculpture forces the figure to bend a leg, while the other remains extended. The arms also have a similar pattern: the position of his flexed right arm is opposed to his extended left arm, while his head and shoulders are rotated, causing the figure to lose his frontal shape and gain more dynamism.
Once again, Michelangelo proves he is both is a connoisseur of tradition and an innovator at the same time. This pose is called "contrapposto" (if an arm advances, the corresponding leg retracts, and vice versa). The figure of the apostle transmits an overwhelming energy that's urging him to overcome the boundaries imposed by matter and free himself.