Sanctify unto me. Not by any positive ceremony, but by regarding it as "set apart unto the Lord" (Exodus 13:12)—made over to him, that is, as his own. All the first-born. The Hebrew word used is masculine, and by its proper force limits the command to the first-born males, who alone had been in danger from the tenth plague.
Whatever openeth the womb. This clause added definiteness, showing that "first-born" did not contain any reference to any later Birth, and that it applied to every case where a woman's first child was a male.
It is mine. Or, "it shall be mine." I claim it.