Feast and Festivals are a part of everyday human life. More than likely the origins of these feast and festivals can be traced back to the societies past religious practices, rituals, or to commemorate an event.
For Muslims, all festivals (and you can't have a festival without a feast) mark the end of an act of worship, and in fact, the festivals themselves are acts of worship, as Muslims intertwine the remembrance of God in every activity. So these days of festivals are not just days for eating and having fun, but they are also days of praising God, remembering his attributes and being extremely thankful to Him for His bounties and blessings.
Islam is based on five pillars. These pillars or acts of worship are obligatory on every Muslim. Two of these acts of worship are Ramadan and Hajj.