Explain two reasons why celebrating Holy
Communion/Eucharist is
important for many Christians,

The Eucharist represents God's new covenant with his people. The ancient covenant was the one God made with Israel when he released them from slavery in Egypt. The new sacrament represents liberation from the servitude of sin as well as the promise of eternal life. So it is very important for many.

The Holy Eucharist refers to the presence of Christ's flesh and blood in the consecrated host on the altar, and Catholics believe that the bread and wine are the literal body and blood, soul and divinity of Christ (which is wickedly erroneous). Communion is considered as a commemoration of Christ's death in most Protestant churches. Because bread and wine are symbols, they do not alter at all.

See this for more info: https://branham.org/en/biblestudy/communion