Notes on Book of Exodus (Author Bishop Richard Challoner (ed.))
13:2 Sanctify unto me every firstborn: Sanctification in this place means that the firstborn males of the Hebrews should be deputed to the ministry in the divine worship; and the firstborn of beasts to be given for a sacrifice.
Original Douay-Rheims from Project Gutenberg - Massive cleanup of OCR problems and editing done locally.