Standing To Pray
It is the custom in our Churches that we stand in worship during the Divine Services.
Anyone who has visited the churches and cathedrals of western Europe knows it was the custom of all of Christiandom to have churches without pews except for the benches provided for the tired, aged, and infirm. Pews are a modern North American phenomenon which has similarly taken hold throughout all of Christiandom, east and west. Sitting is acceptable during Bible readings (except for the Gospel when we stand if we’re able), the chanting of the Psalms, during the litanies, and the sermon. Despite the pews, we continue to stand throughout most of the Liturgy, and it is never wrong to stand on a Sunday.
The west developed a tradition of kneeling within a culture which showed respect and subservience by kneeling before authority. Think of a Medieval English knight kneeling before the king and you will recognize this cultural posture. The western secular symbolism of kneeling was enculturated into the western church which shows allegiance, deference, and respect to the Lord in the same way they show allegiance to their earthly lords.
Some Eastern Christian churches, both Catholic and Orthodox, have been influenced by geographic proximity to western Christians who kneel on Sundays. It is not uncommon to see Eastern Christians kneeling because of this influence.
Just as we have a secular tradition of standing to show respect when a lady or one’s superior enters the room, the east traditionally shows respect and subservience to God by standing in attention and awe. Think of Christ reclining on cushions at the table while attendants stand around ready to serve Him. Kneeling is reserved in the east for times when one throws oneself on the mercy of the Lord, just as Jairus and the afflicted woman did near Decapolis (Mark 5:21-32). We prostrate ourselves before God during penitential seasons and fasts. On Sundays, we stand and celebrate the Resurrection in deference, respect, and awe.
Kneeling is actually forbidden on Sundays and every day from Pascha (Easter) to Pentecost by the First Ecumenical Council in Nicea and the Quinsext Council in Constantinople, both of which occurred when standing was the custom of the undivided church. We continue this tradition today.
First Ecumenical Council (Nicea, 325 AD) Canon 20

Since there are some persons who kneel in church on Sunday and on the days of Pentecost, with a view to preserving uniformity in all parishes, it has seemed best to the holy Council for prayers to be offered to God while standing.

(c. XC of the 6th; c. XV of Peter.)

Quinisext Council (Constantinople, 692 AD)

We have received from our divine Fathers the canon law that in honour of Christ’s resurrection, we are not to kneel on Sundays. Lest therefore we should ignore the fullness of this observance we make it plain to the faithful that after the priests have gone to the Altar for Vespers on Saturdays (according to the prevailing custom) no one shall kneel in prayer until the evening of Sunday, at which time after the entrance for compline, again with bended knees we offer our prayers to the Lord. For taking the night after the Sabbath, which was the forerunner of our Lord’s resurrection, we begin from it to sing in the spirit hymns to God, leading our feast out of darkness into light, and thus during an entire day and night, we celebrate the Resurrection.