Because that alms do deliver from death, and suffers not to come into darkness.
Read Chapter 4
Augustine of Hippo
“Light has arisen for the just person.” What light is there for a just man or woman? A certain light that does not rise for the unjust, different from the light that dawns on good and bad alike. Another light rises on a righteous person, that light of which the unrighteous will confess at the end that it never dawned for them: “No doubt of it, we strayed from the path of truth. On us the light of righteousness did not shine, nor did the sun rise for us.” Reveling in the common light, they lay in darkness of heart. What did it profit to them to see daylight with their eyes, if their minds could not see the light beyond? Tobit was blind, yet he taught his son the way of God. You know this is true, because Tobit advised his son, “Give alms, my son, for almsdeeds save you from departing into darkness,” yet the speaker was in darkness himself. Do you see from this that it is a different light that rises for a just person and good cheer for those of straightforward heart? - "Expositions of the Psalms 96.18"