Commentary Par X 49-51

Dante refers to those who show themselves in the Sun, the fourth of the planets, as the 'fourth family'; God makes them happy by demonstrating his other two Trinitarian aspects, Wisdom (manifest in the Son) and Love (present in the Holy Spirit).  See the opening of this canto ([Par X 1-3]).

If the preceding six verses described Dante's inability to portray the brightness of God's creatures, this tercet proclaims God's 'art' in demonstrating His triune nature.