Annual festivals are a way of understanding the cultural context of a given place. It also helps establish the rhythms of a community.
In Milwaukee and SE Wisconsin, there is a rhythm to the seasons, there is winter (8-10 months out of the year) and summer festivals. The plural is important, there is the 'Summerfest' and then there is Germanfest, Irishfest, Scotishfest, etc. It helps set a pattern of celebration for the communities that make up the SE Wisconsin area.
In the same way, God provides 3 annual festivals for observance by God's people. The festival of unleavened bread celebrated the deliverance from Egypt, when God provided manna from heaven along their journey. The festival of Harvest is a harvest festival that gives back to God first givings of what all that God provides. The festival of final harvest to celebrate the abundance God has provided for God's people that year.
All 3 are important in the life of the community because "At these three times each year, every man in Israel must appear before the Sovereign, the Lord." Each festival marked God's presence within the community and their celebration of relationship.