Well, one of my favourites, because it's good for a laugh. I'm sure there are some good explanations out there but I haven't heard one.
For his ride into Jerusalem, Matthew describes how Jesus tells his disciples to fetch an ass and a colt, to fulfill an Old Testament prophecy:
Matthew 21:2,4,5,7 Saying unto them, Go into the village over against you, and straightway ye shall find an ass tied, and a colt with her: loose them, and bring them unto me. All this was done, that it might be fulfilled which was spoken by the prophet, saying, Tell ye the daughter of Sion, Behold, thy King cometh unto thee, meek, and sitting upon an ass, and a colt the foal of an ass. And brought the ass, and the colt, and put on them their clothes, and they set him thereon.
But the prophecy that Matthew quoted only refers to one animal:
Zechariah 9:9 Rejoice greatly, O daughter of Zion; shout, O daughter of Jerusalem: behold, thy King cometh unto thee: he is just, and having salvation; lowly, and riding upon an ass, and upon a colt the foal of an ass.
The word ‘and’ in this sense means ‘even’, which is how it is used elsewhere in the Old Testament and how it is translated in other bible versions - the second phrase is an interpretation of the first.
Matthew misunderstood the OT prophecy and thought that Jesus was to sit astride two animals as he rode into town. It’s comical, but it isn’t the infallible word of God. Or is it?
(The other three gospel writers only have one animal.)
The passage in Matthew is pointing out the literal fulfillment of the prophecy of Zechariah 9:9 which states, "Behold your king is coming to you. . . humble, and mounted on a donkey, even on a colt, the foal of a donkey."
This is the part I have a problem with. This prophecy clearly states one animal. The other three gospel writers read it as such. It seems to me that Matthew misinterpreted the prophecy and thought there were two animals.
The issue here isn't really how silly Jesus looked riding two animals - I'm sure Matthew didn't mean to imply that (it's just fun to poke fun); it's whether Matthew misinterpreted the prophecy. Considering the similarity of his wording and that in Zechariah, it seems that he did.