Palm Sunday commemorates the triumphal entry of Jesus into Jerusalem (Matthew 21:1–11, Mark 11:1–11, Luke 19:28–44, John 12:12–19) and opens Holy Week. All four Gospels record the event: Jesus riding into the city on a donkey in deliberate fulfillment of Zechariah 9:9, the crowds spreading garments and branches on the road, and the acclamation 'Hosanna to the Son of David! Blessed is he who comes in the name of the Lord!' The palm branches, mentioned explicitly only in John's Gospel, gave the day its name; the other Synoptic writers mention 'branches cut from the fields' (Mark 11:8) or 'their cloaks' (Luke 19:36). The liturgical observance is ancient. The pilgrim Egeria, writing around 384, provides the earliest detailed description of a Palm Sunday procession in Jerusalem: the bishop rode from the Mount of Olives into the city while the people carried palm and olive branches, and children too young to walk were carried on their parents' shoulders, all singing 'Blessed is he who comes in the name of the Lord.' This Jerusalem stational liturgy — procession from a site outside the city through the gates — became the model for Palm Sunday observances throughout Christendom. By the seventh century, the practice had spread throughout the Western churches. The Bobbio Missal (7th c., Gallican rite) attests Gallican influence on the introduction of palm blessing into Western liturgy, and the ninth-century Romano-Germanic Pontifical codified the full Western pattern of palm blessing, procession, and Passion Gospel that persists in recognizable form to this day.

Palm Sunday is unique among liturgical days in sustaining two contrasting moods within a single service. The BCP 2019 preserves this ancient pattern: the liturgy begins outdoors (or at a station apart from the main church) with the blessing of palms, the reading of the Triumphal Entry Gospel, and a procession into the church with hymns of praise — typically 'All Glory, Laud, and Honor' (Theodulph of Orléans, 820). But once the congregation enters the church, the tone shifts sharply. The Eucharistic Gospel is the full Passion narrative from one of the Synoptic Gospels (rotating by lectionary year: Matthew in Year A, Mark in Year B, Luke in Year C — John's Passion is reserved for Good Friday). The congregation that moments ago cried 'Hosanna' now speaks the words of the crowd calling for crucifixion. This liturgical reversal — from royal welcome to the demand for blood — enacts the central paradox of the Passion: the King who was received with palms was dead by Friday. The BCP's introductory rubric makes the theological point explicit: 'We who hail Jesus as King one moment, may in the next deny him, even joining with the crowd in shouting, "Crucify him!"' The color is red — for the Passion, not for Pentecostal fire. Some parishes use violet through the early days of Holy Week and switch to red for the Triduum, but Palm Sunday itself takes red because the Passion Gospel dominates the Eucharistic liturgy. The palms distributed to the congregation have generated their own devotional tradition: many Christians keep their palms throughout the year, and the custom of burning the previous year's palms to produce ashes for Ash Wednesday creates a beautiful liturgical cycle linking the two days.

According to the Armenian historian Agathangelos, Gregory was born the son of Anak, a Parthian nobleman who assassinated the Armenian king Khosrov II. The infant Gregory was smuggled out of Armenia and raised as a Christian in Caesarea in Cappadocia, where he was baptized and educated.

As an adult, Gregory returned to Armenia and entered the service of King Tiridates III, seeking to atone for his father's crime. When Gregory refused to offer sacrifice to the goddess Anahit, Tiridates subjected him to prolonged torture and eventually threw him into a pit — Khor Virap ('deep prison'), near Mount Ararat — where he languished for thirteen years, sustained by a widow's secret supply of bread.

Meanwhile, Tiridates was afflicted with a mysterious illness (tradition describes him being transformed into a wild boar) that no physician could cure. His sister dreamed that only Gregory could heal the king. Gregory was brought from the pit, healed Tiridates (through prayer, not medicine), and the king was converted. Armenia officially adopted Christianity around 301 — a century before most of the Christian world.

Gregory was consecrated bishop by Leontius of Caesarea and systematically destroyed pagan temples and built churches across Armenia. He established his see at Etchmiadzin, where the cathedral he founded remains the spiritual center of the Armenian Church. After organizing the church, he withdrew to a hermitage and died around 331.

Gregory's descendants served as Catholicos (chief bishop) of Armenia for generations, establishing a hereditary ecclesiastical dynasty.

Traditionally, Gregory's thirteen years in Khor Virap were sustained by divine providence — a pious widow secretly brought him daily bread without anyone discovering her. His emergence from the pit, healthy and luminous, was taken as a miraculous sign. According to Agathangelos, Gregory had a vision in which Christ descended from heaven and struck the ground at Etchmiadzin with a golden hammer, marking the site of the mother cathedral.