These three types of learning are precepts, concentration, and wisdom. Precepts (or morality) are for the sake of correctly training mind and body and establishing correct physical and mental habits. Concentration, or meditation, is for the sake of spiritual unification after the mind and body have been properly trained. It produces a state in which the mind is as clear as a mirror and as still as the surface of an undisturbed body of water. Correct wisdom, reached when this kind of spiritual unification has been attained, makes possible correct judgments and suitable actions. In the light of this progression, the order for training and attainment in the three types of learning is this: precepts, concentration, and wisdom.
But, since the three types of learning correspond to three aspects of the human spirit—intellect (wisdom), emotion (concentration), and volition (precepts)—and since all three of these exist simultaneously as parts of the human spirit, the three kinds of learning, too, are not independent of each other but form a unity. From this viewpoint, there is no question of precedence among them. Nonetheless, for the sake of attainment of the states toward which the three kinds of learning are directed, the order precepts, concentration, and wisdom is reasonable.
The Beginnings of Buddhism