What does "gird one's loins" mean?

Also, gird up one's loins. Prepare oneself for action, as in I'm girding up my loins for that crucial interview. This expression comes from the Bible (Proverbs 31:17) and originally alluded to tucking up the traditional long robe into a girdle (that is, a belt) so it will not hamper physical activity. [c. 1600]