The Scofield Bible Commentary, by Cyrus Ingerson Scofield, [1917], at sacred-texts.com
Let my people
Compare (Exo 4:22); (Exo 4:23).
Possibly Moses and Aaron shrank from delivering the message concerning the firstborn.
three days
Compare (Mat 12:38-40).
By death and resurrection will God have his people separated from Egypt -- the world. (Rom 6:1-11); (Gal 6:14-15); (Heb 13:12); (Heb 13:13).