The phrase "if one curses his father and his mother" raises yet another question: with what name must the curse be spoken? Rabbi Achai taught that the offender is liable for the death penalty only if he curses his parents using the explicit Name of God — the Tetragrammaton, the four-letter divine Name.
But perhaps cursing with a mere epithet — a descriptive title for God rather than the actual Name — would also be sufficient? The Mekhilta rejects this through a cross-reference to (Leviticus 24:16): "When he blasphemes the Name, he shall be put to death." The mention of "the Name" specifically — not merely a reference to God — establishes that capital liability requires the use of the explicit divine Name.
The seemingly redundant phrase in Leviticus was not written merely to address blasphemy in general. It was written to include the case of one who curses his parents. Without it, we might have thought that any invocation of God's name — even an epithet — would trigger the death penalty. The specification of "the Name" narrows the scope to the Tetragrammaton alone.
This ruling had the practical effect of making the death penalty for cursing parents extremely difficult to carry out. The offender had to use the specific four-letter Name, in the presence of witnesses who could testify to exactly what was said. Anything less than the explicit Name — any euphemism, abbreviation, or descriptive title — would not meet the legal threshold for execution.