«اِلْجَيِّدَهْ فِي خِيلَكْ اِلْهَدْهَا»

The saying advises putting your finest resource to hard use. The 'good one' here is the best-bred mare, and the closing verb means to exert her by riding hard. Such a mare can be pushed without harm and will carry her rider quickly to his goal.

The image is about trusting strength, not about mistreating animals. Whatever is most capable, whether a tool, a helper, or a skill, should carry the heaviest load when a goal matters, because quality can endure strain that would break something inferior.

Fits advice to someone weighing which means to rely on. It urges them to pick their strongest option and use it fully rather than saving it, because a capable resource can bear heavy demands and will deliver results.