ISB ~ Matthew 21 v7

he sat on them:Matthew alone mentions a donkey and a colt (cf. Mk 11:7; Lk 19:35). That Jesus sat on them refers either to the garments or indicates that he rode both beasts successively.

• Allegorically (St. Jerome, Homily 81): the two beasts are the nations that Christ brings under his Lordship. The donkey signifies Israel in its long-standing covenant with God; the colt is the younger Gentiles, unfamiliar with God and his Law. Jesus ushers them together into the Church of the heavenly Jerusalem (Gal 4:26; Heb 12:22).