Sunday 9 Nisan is when Jesus entered Jerusalem. This is the day we commemorate as Palm Sunday because Jesus fulfilled prophecy that the Messiah would enter Jerusalem riding a colt. Now it is called a triumphal entry because this is the first time Jesus publicly declared he was King of the Jews (Zechariah 9:9). This day is quite important because it fulfilled the prophecy made by Daniel many years ago about the Messiah. It was through that prophecy that the wise men were able to calculate the birth of the Messiah – they knew if a guy was to declare himself King around that time, he would have to be born x number of years before.
After riding into Jerusalem, Jesus checks into the temple. Now if we go back to our summary of the feast of the passover, you will recall that God instructed Moses to parade the chosen lamb in the temple where he was to be examined for defects for the next 5 days before it was sacrificed. On the very same day the lamb was paraded in the temple, Jesus paraded through the streets of Jerusalem. He thus presented himself in the temple on the same day, satisfying this aspect of the law of Moses.