[The Sun Says:]

The sun and moon stood still in their abodes,

[Yisrael] would travel by the light of Your arrows,

by the brightness of Your gleaming spear.

(Chavakkuk 3:11)

The sun is a symbol of respect for G-d and generosity to others.  Arrows and the spear of G-d is lightning bolts.  HaShem cast lightning bolts and hailstones upon Yisrael's enemies, who fled before the B'nei Yisrael.  Both the sun and the moon are mentioned, yet in the singular form of "stood" is stated.  In the future, the sun and moon will enjoy the same stature.  The Chazal teach that they will shine with equal brightness, just as they did at the time of their creation.
[MeAm Lo'ez, Perek Shira]