The sun and moon stood still in their habitation: at the light of thine arrows they went, and at the shining of thy glittering spear. The sun and moon stood still - This was at the prayer of Joshua, when he fought against the Amorites. See Joshua 10:11-12 (note), and the notes there.
At the light of thine arrows they went - I think we should translate: -
By their light, thine arrows went abroad; By their brightness, the lightning of thy spear.
Calvin very justly remarks that the arrows and spears of the Israelites are called those of God, under whose auspices the people fought: the meaning is, that by the continuation of the light of the sun and moon, then stayed in their course, the Israelites saw how to continue the battle, till their enemies were all defeated.