To kneel on sundays has been prohibited by the CATHOLIC CHURCH, as gathered at the 1st Ecumenical Council, and promulagated by the Council and the Pope, ***for over 1600 years. ***
At some point, Rome decided to ignore that canon. So be it.
From the Divine Liturgy of St. John, at the beginning of the anaphora (consecration):
“Let us Stand Aright, let us stand in awe, let us be attentive, to offer the Holy Oblation in peace!”
The Byzantines have kept their tradition and the canons of Nicea. Arrogance is believing that Roman posture is motivated out of humility any more. (And those most vocal about it tend to use it as a point of pride, no less!)
Most of the Romans I know attribute no particular meaning to kneeling, other than obedience to the rubrics… it says kneel, so they do. It says stand, so they do. The Roman liturgy is a poor tool for teaching the faith. It never says why we do the things we do. It merely lists what must be done. But catechesis is abysmally poor about the Roman Mass, in either form.
The Byzantine liturgy (and the Coptic Liturgy, as well) is a teaching tool as well as worship. It tells us about how and why we stand: We stand aright, we stand in awe, we stand to pay attention, because we begin the holiest prayer in all Christian worship.
You want the Byzantine theology? you grab the Irmologion and the Menaion. It’s all there, and it is used in the liturgy. And kneeling is sorrowful, or so the Troparia, Kontakia, Irmosi, and other propers teach. If we do not stand in awe, we fall to the ground in awe and hide our faces.
We should NEVER be Sorrowful when celebrating the Resurrection! Shout with Joy and be Glad! Christ is Risen!