While Palm Sunday is a good time to remember this, it's worth noting that the acceptance of Jesus into Jerusalem was not a one-time event. It's not something we merely remember each year the Sunday before Easter for old times' sake. We become that crowd who welcomes Christ into our Jerusalem, our temple, every time we attend Mass.
Consider this portion of the Eucharistic prayer:
“Holy, holy, holy Lord. God of power and might. Heaven and earth are full of your glory. Hosanna in the highest! Blessed is he who comes in the name of the Lord. Hosanna in the highest!”The first part (holy, holy, holy) shows that we are worshiping with the saints and angels in heaven because that's their prayer from Revelation. The italicized part is precisely what the crowd proclaimed as Jesus entered Jerusalem. We say this because Jesus didn't only come into Jerusalem so many years ago but he comes into our local church today, each and every time we celebrate Mass. We don't just remember “how cool it must have been” but we are present as he approaches right before our eyes. We aren't just remembering; we are experiencing.
Just as the people in Jerusalem recognized Jesus in the prophesy that their king would come to them riding on a donkey (Zec 9:9) so we should recognize Jesus by his own word; that he is the bread and wine (Lk 22:19-20). Jesus doesn't stop at the altar, however, but enters us as we consume him. He enters our bodies, the “temple of the holy Spirit”.
Palm Sunday is a great time to wonder what it would have been like to live when Jesus was walking the earth but we need to remember he had no more glory, divinity, or greatness then than he has when he comes to us in the Mass!