Horses were obtained from Egypt, and buying horses might have required going to Egypt and even settling there, which the Torah forbids (Deut. 28:68). King Solomon disobeyed this command and stationed agents in Egypt who built up an export trade in horses (I Kings 10:28).
Nachmanides explains that the problem with horses was not only the Egyptian connection but the fear that a king who had many horses would put his trust in them instead of in God.
The Psalmist warned, “God delights not in the strength of the horse… He takes pleasure in them that revere Him” (Psalm 147:10-11). The Psalmist also says, “A horse is a vain thing for safety, nor does it afford escape by its great strength” (Psalm 33:17).
But in the domestic context the horse was highly prized. The horse was used for riding, for carrying loads, and for other useful purposes. Covers and blankets were made of its hair. Though its meat was not kosher, non-Jews ate it. A person should not live in a town where the neighing of the horse was not heard (Pes. 113a).
All this reminds us that whatever God has given us is ours to use… but our possessions should never become our masters or our idols.