I post two separate entries on Dante because while they abut one another in the poetry, they seem to go separate directions in thought. And this particular point is one that a lot of people have difficulty remembering because this world is so limited.
from Purgatorio Canto XV
Dante (tr. John Ciardi)
"How can each one of many who divide
a single good have more of it, so shared,
than if a few had kept it?" He replied:
"Because within the habit of mankind
you set your whole intent on earthly things,
the true light falls as darkness on your mind.
The infinite and inexpressible Grace
which is in Heaven, gives itself to Love
as a sunbeam gives itself to a bright surface.
As much light as it finds there, it bestows;
thus, as the blaze of Love is spread more widely,
the greater the Eternal Glory grows.
As mirror reflects mirror, so above,
the more there are who join their souls, the more
Love learns perfection, and the more they love.
If you visit colonial houses, you will often find on the wall sconces with convex mirrors or polished surfaces behind them. The purpose was to capture the light from a single candle and use it more efficiently. And so Dante's metaphor. Love that falls on a surface ready to receive it both lights that surface to the degree that it is prepared to be lit, and is "multiplied" to reflect from other such surfaces. Love, as we are well aware, does not diminish in the division, but paradoxically, multiplies. The metaphor of reflection is a clear and perfect trope for the activity of love.