A feast is engineering, built to put joy into people whose circumstances would never hand it to them.
Joy can be commanded only because it is produced on purpose. Keep the date, set the table, gather the household, and the body is doing work that waiting for good news never gets around to; the shared table pulls focus off the year's shortfalls, and the emotion follows the room a person is standing in.
Seating the servant, the foreigner, the fatherless and the widow inside the same rejoicing is deliberate design: the people with the least material reason for joy are placed in the conditions that manufacture it instead of being left to find it alone. A household that waits to feel festive celebrates rarely, and the ones carrying the most are the last anybody thinks to include.