What does Matthew 21:4 mean?
Before entering Jerusalem, Jesus has sent two disciples to pick up a donkey and her colt form a nearby village. He has prearranged this and let the disciples know that the animals will be waiting for them there. Jesus will ride the colt into Jerusalem instead of walking (Matthew 21:1–3).This was to fulfill a specific prophecy about the Messiah. The prophet in question is Zechariah (Zechariah 9:9), though a similar statement is also found in Isaiah (Isaiah 62:11). Matthew's reference could be attributed to either. Unlike most prophecies fulfilled by Jesus, Matthew is clear that Jesus orchestrated this one personally. Commentators refer to it as an "acted parable," meaning that Jesus is intentionally demonstrating to the crowds that He is the Messiah.
Prior to this moment, Jesus has been cautious about making His identity as Messiah widely known (Matthew 16:20; Mark 8:30). John, in his gospel, points out that this is because Jesus knows the time is not yet right for that news (John 2:4; 7:8). The people were likely to misunderstand (John 6:15). Now, however, it is time for Christ to openly claim His title (Matthew 21:9).