Cardinal virtues
Augustine of Hippo, discussing the morals of the church, described them:
The "cardinal" virtues are not the same as the three theological virtues: Faith, Hope and Charity (Love), named in 1 Corinthians 13. 
"And now these three remain: faith, hope and love. But the greatest of these is love."
Because of this reference, a group of seven attributes is sometimes listed by adding the four cardinal virtues (prudence, temperance, fortitude, justice) and three theological virtues (faith, hope, charity).
Together, they comprise what is known as the seven virtues. While the first four date back to Greek philosophers and were applicable to all people seeking to live moral lives, the "theological virtues" appear to be specific to Christians as written by Paul in The New Testament.
T. K. Seung
Seung elucidates the poem's thematic unity by using three principles essential to medieval Christian thinking. The first principle is the medieval classification of virtues and sins. It provides the framework for understanding the formal structures of the three realms. Seung shows that Hell, Purgatory, and Paradise are structured in accordance with the medieval table of seven natural virtues and three supernatural virtues, which are implicitly celebrated in the ten spheres of Paradiso. The natural virtues are humility, mercy, meekness, fortitude, liberality, temperance, and chastity, and the supernatural virtues are the three theological virtues of faith, hope, and love. The contraries to the natural virtues are the seven deadly sins of pride, envy, wrath, sloth, avarice, gluttony, and lust, and they are condemned as sinful acts in the various sections of Inferno, and on the seven terraces of Purgatorio they appear as vicious dispositions being purged into their virtuous opposites. Moreover, in the beginning of Inferno the supernatural virtues are thematized as being absent; in the beginning of Purgatorio they appear as distorted; near the end of Purgatorio they are celebrated as regained; and finally in the last cantos of Paradiso they are presented in full display.