Generally I don't read the NIV translation, however it's one of the few that uses the word "spur" which obviously connects to horses. In place of "spur," other translations use provoke, stimulate, stir up, encourage, and spark. The idea is to motivate or prompt to action.
Many think it's cruel to use spurs on horses - and it can be if used improperly. Used correctly, spurs actually allow the rider to give more subtle and precise cues using a lighter touch.