Allusion is here made to a peculiar form of sun-worship. Among the Persians horses were considered sacred to the sun. The king of Persia when be sacrificed offered a white horse to that luminary. The people, when they wished to sacrifice to the sun, mounted their horses in the early morning and rode toward the rising orb as if to salute it, and then offered the noble victims to it in sacrifice. See Gale's Court of the Gentiles, chap. 8, p. 115.
The kings of Judah had evidently heard of this custom, and imitated it; though some commentators doubt that they actually slew the animals, supposing that they simply went in state in the early morning to see the sun rise and to adore it. Some have even imagined that these horses were not real, but merely statues, made of wood, stone or metal, which stood at the entrance of the temple. The mention made of the “chariots of the sun” in the latter part of the verse seems, however, to indicate that living animals were intended, and that they were harnessed to these chariots. Whether they were really sacrificed or not, they were kept and used for idolatrous purposes, and therefore became proper subjects of confiscation.