Matthew 21:7

And put on them their clothes] either because they were uncertain which one He intended to mount, or in order gaily to caparison both animals for the procession. Eastern garments are brightly coloured. And they set him (RV 'he sat') thereon] i.e. on the clothes placed upon the colt, not, as some take it, that He rode upon both animals alternately.

By riding upon the ass Jesus deliberately fulfilled the prophecy of Zechariah, and so claimed to be the Messiah. The ass was chosen rather than the horse, because the ass was a symbol of peace, the horse of war; the ass of humility, the horse of pride. The Jews fully accepted the Messianic reference of Zechariah 9:9. Rabbi Salomo said, 'This cannot be interpreted except of Bang Messiah.'