Because all the firstborn [are] mine; [for] on the day that I smote all the firstborn in the land of Egypt I hallowed unto me all the firstborn in Israel, both man and beast: mine shall they be: I [am] the LORD.
Jewish Publication Society of America Version (JPS1917) - Numbers 3:13 >for all the first-born are Mine: on the day that I smote all the first-born in the land of Egypt I hallowed unto Me all the first-born in Israel, both man and beast, Mine they shall be: I am the LORD.'