Charles Ellicott Commentary Exodus 12:29

"And it came to pass at midnight, that Jehovah smote all the first-born in the land of Egypt, from the first-born of Pharaoh that sat on his throne unto the first-born of the captive that was in the dungeon; and all the first-born of cattle." — Exodus 12:29 (ASV)

All the firstborn. —The Hebrew word used applies only to males.

The firstborn of Pharaoh. —The law of primogeniture prevailed in Egypt, as elsewhere generally. The Pharaoh’s eldest son was recognized as “hereditary crown prince,” and sometimes associated in the kingdom during his father’s lifetime. This had been the case with Rameses II, probably the Pharaoh from whom Moses fled (Exodus 2:15); but the practice was not common. In any case, however, the eldest son of the reigning monarch occupied a most important position, and his loss would be felt as a national calamity.

The firstborn of the captive. —The variation of phrase between this verse and Exodus 11:5 is curious, but appears not to be of any significance. The writer simply means, in both places, “all, from the highest to the lowest.”

All the firstborn of cattle. —Rather, of beasts, as in Exodus 11:5. (On the reasons for beasts being included in the calamity, see the Note on that passage.)