How we cite our quotes:
[Justinian]: "This little planet is adorned with spirits,
whose acts were righteous, but who acted for
the honor and the fame that they would gain;
and when desires tend toward earthly ends,
then, so deflected, rays of the true love
mount toward the life above with lesser force." (Par. VI, 112-118)
Justinian gives the reason why the inhabitants of Mercury are not more blessed than they are. On earth, they "acted for the honor and fame they would gain." This means they loved honor and fame more than they did God. These are lesser "earthly ends" and, upon their deaths, God placed them in a relatively low sphere of blessedness to match their somewhat petty desires.
[Beatrice]: "for God showed greater generosity
in giving His own self that man might be
able to rise, than if He simply pardoned;
for every other means fell short of justice,
except the way whereby the Son of God
humbled Himself when He became Incarnate." (Par. VII, 115-120)
After Adam's original sin, God could have simply sent everyone to Hell. However, his generosity or compassion allowed man another way out. Out of his infinite love, God gave Himself to man in the form of Jesus Christ, and through faith in him, allowed man a way to access Heaven again. That God's sacrifice is considered "justice" implies that earthly justice should, like God's, include a measure of mercy.
[Dante to Charles Martel]: "…so may you clear the doubt
that rose in me when you – before – described
how from a gentle seed, harsh fruit derives."[…]
[Martel]: "The Good that moves and makes content the realm
through which you now ascend, makes providence
act as a force in these great heavens' bodies;
and in the Mind that, in itself, is perfect,
not only are the natures of His creatures
but their well-being, too, provided for;
and thus, whatever this bow shoots must fall
according to a providential end,
just like a shaft directed to its target.
Where this not so, the heavens you traverse
would bring about effects in such a way
that they would not be things of art but shards." (Par. VIII, 91-108)
In answering Dante's question of why good fathers sometimes have evil or unjust sons, the key word is "providence." Providence sanctions all the little hiccups in the universe that do not seem to make sense. It is considered a form of divine love because everything it does is in the interest of "His creatures'…well-being." So even evil sons begotten from good fathers have a role to play in the world that will ultimately benefit man's well being.