From the early Church Fathers to now.
“And a man that is clean shall gather up the ashes of the cow, and shall pour them forth without the camp in a most clean place, that they may be reserved for the multitude of the children of Israel, and for a water of aspersion: because the cow was burnt for sin.”
“And again: "The water of sprinkling is a purification." Whence it appears that the sprinkling also of water prevails equally with the washing of salvation; and that when this is done in the Church, where the faith both of receiver and giver is sound, all things hold and may be consummated and perfected by the majesty of the Lord and by the truth of faith.”
The in-app commentary runs from the Fathers to the early-modern record, then stops — that's where the public-domain sources end, not where the reading does. For the modern reading, follow the sources directly.