To the end, for the eighth, a psalm of David.
1. It has been said on the sixth Psalm, that “the eighth” may be taken as the day of judgment. “For the eighth” may also be taken “for the eternal age;” for that after the time present, which is a cycle of seven days, it shall be given to the Saints.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)