Would that I could see the Opener of the Ways in his first procession when he gleams as a god... and Heru the vigorous, who gladdens the people as he passes along the canals leading to the Great Hall

The Passion Plays of Wesir at Abedjou were held in the last month of the inundation, the fourth month of Akhet, and included eight acts. These celebrations relied on the myth of the murder of Wesir by his brother Set, and how his sister-wife Aset managed to restore him to life again. The reason for them beingheld at Abedjou, was that this ws the traditional place where the body of Wesir drifted ashore after having been drowned in the Nile.The story of how his body was chopped up by Set and his helpers, is a lateer addition, not having been found before Plutharch.

The exact procedures are largely unknown. It is believed that there were great celebrations among people combined with secluded, sacred rituals performed by the priesthood inside the temple. Part of these rites were public however, and the processions which emerged from the temple were attended by masses of commoners. Perhaps the most important reason for the widespread popularity of the Cult of Wesir was the promise of eternal life to each and everyone, commoner and king alike.

Thousands of pilgrims from all parts of the Two Lands assembled yearly at Abedjou near the great temple to celebrate the mysteries. It was the desire and duty of every Egyptian to make a pilgrimage at least once in his life, to Abedjou. It is believed that people in the town divided up into two camps and acted out the murder of Wesir by Set, Aset´s sorrow and anger, her wanderings together with her sister Nebt-Het, to find her dead husband, the funeral and, finally, his resurrection as the Lord of the Dead. (The story of the dismemberment didn´t enter the picture until the Late Period, when Plutarch set it down.)

Inside the temple enclosure, secluded rituals were performed, with the priests and godservants playing the parts of the different gods, and occasionally the King himself partook. The celebrations went back thousands of years, tradition bringing the sense of stability and eternity.

They focused on the resurrection of Wesir and how he became the ruler of the kingdom of the deceased, (the 'Field of Reeds'), where the dead lived the same life as on earth. This was made possible thanks to the kingship of Wesir, and so the deed of Set was turned into benefit for all humans instead of remaining a murder of a King by a jealous brother.

The cult of Wesir and the acting out of these rituals by the priesthood became an important pendant to other rites such as the coronation and the Heb Sed Jubliee. In this way the cult of Wesir helped celebrate and maintain the power of kingship. By acknowledging Wesir as the king of the dead, and Heru, his son and heir as king of the living, they sought also to ensure the return of the yearly inundation, a plentiful harvest and, in fact, the perpetuation of Egypt on two planes - for the dead and for the living.

Some information of the proceedings of the Passion Plays of Wesir can be gleaned from a Middle Kingdom stela, which describes how a high official by name of Ikhernofret is given the task by the King to organize the Festival processions.

The First Day - The Procession of Wepwawet:

Wepwawet opens the way of the procession. The enemies of Wesir is struck down in a mock battle. It seems an assault was staged by the 'followers of Set', this assault was to be struck down, either by priests or by pilgrims acting the 'followers of Wesir', or perhaps by both. Likely it was acted out both on in the temple courtyards and outside, in the village streets. This might have been a way to commemorate the "Contendings of Horus and Set".

The jackal-god Wepwawet who is walking foremost in all royal processions and conquests, goes by the name of 'Opener of the Way'. In that context he opens the path for Wesir to gain access to the tomb.

The Second Day - The Great Procession of Wesir

The deceased Wesir, carried on a bark called 'Neshmet' ('night bark which Re rides in every night) is taken from his temple to his tomb. The procession moves through the surrounding cemetery grounds to the tomb (it seems they take a tour out in the desert before ending up at the Osireion). The Lamentations of Aset and Nebt-Het are performed by women impersonating the goddesses. There would be two women impersonating Aset and NEbt-Het, wandering around the temple premises and the village, looking for the body of Wesir. When they found him on the "riverbank", they would sit down and recite the Lamentations. In Pap. Berlin no 3008, the instructions for the Lamentations say:

During this night´s reenactment, the enemies of Wesir are slain on the 'banks of Nedyet' (the tomb) and the night ends with the trial of Set before the Divine Tribunal.

The Third Day - Wesir is Mourned and the Enemies of the Land are Destroyed.

Mourning and weeping are continued. At the same time, there were probably secluded rituals in which a serpent and an ass, symbolizing Apep and Set, were destroyed, thereby making the country safe from their danger. It´s not clear wether these animals were offered as a fact, or if there were only statues of them.

The Fourth Day - Night Vigil

During the Night Vigil there were prayers and recitations performed before the statue of Wesir. Priests and priestesses played parts in the reenactment and actual funeral rites were also performed.

The Fifth Day - Wesir is Reborn

The god was reborn at dawn and crowned with the crown of Ma'at. The statue of Wesir on the Neshmet bark is brought back in triumph to his temple, followed by the jubilant masses. Purifications and reinstallment of the god in his House followed and before the rites were concluded, the ritual of the 'Raising of the Djed-pillar' took place. This last part was not open to the public however.

When the festival was concluded, the pilgrims usually offered something to the god, maybe dried alluvium, a small statuette, even a shrine or, if they were rich or kings, an entire temple.

Many pilgrims also erected stela on the grounds or at the outer precincts of the temple to be able to witness the Mysteries also after they themselves had 'Gone West':

I would be among the crowd following Wesir when he appears in his final form, praising the god and singing in adoration of the beauty of the Neshmet Barqe, fetching the rudder for the boat and honouring the Great God

Sources:

Guide to Religious Ritual at Abydos - A. Rosalie David
The Ancient Egyptians; Religious Beliefs & Practices - A. Rosalie David
The Complete Temples of Ancient Egypt - Richard H. Wilkinson
Cultural Atlas of Ancient Egypt - John Baines & Jaromir Malek