“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.”
Canon 20 of the 1st Ecumenical Council of Nicaea
This Canon is repeated in Canon 90 of the Sixth Ecumenical Council with more explanation as to the reason for the Canon:
“90. We have received it canonically from our God-bearing Fathers not to bend the knee on Sundays when honoring the Resurrection of Christ, since this observation may not be clear to some of us, we are making it plain to the faithful, so that after the entrance of those in holy orders into the sacrificial altar on the evening of the Saturday in question, let none of them bend a knee until the evening of the following Sunday, when, after the entrance during the Lychnic, again bending knees, we thus begin offering our prayers to the Lord. For inasmuch as we hare received it that the night succeeding Saturday was the precursor of our Savior’s rising, we commence our hymns at this point spiritually, ending the festival by passing out of darkness into light, in order that we may hence celebrate en masse the Resurrection for a whole day and a whole night.”
Finally, I want to consider a Canon of similar import relating to Saturday:
“55. Since we have learned that those in the city of the Romans during the holy fast of Lent are fasting on the Saturdays thereof, contrary to the ecclesiastical practice handed down, it has seemed best to the holy Council for the Church of the Romans to hold rigorously the Canon saying: ‘If any Clergyman be found fasting on Sunday, or on Saturday, with the exception of one only let him be deposed from office. If, however, a layman, let him be excommunicated.'”
The way of Life in Christ is the way of the Cross. It is the ascetic way, not only for monks but also for all laity. It is the way of humility and entreating God’s mercy on bended knees and prostrating oneself before the King of Heaven, as unworthy servants. This is a constant reminder of our sins and the Holy Majesty of God.
However, on Sunday something different happens. We are to stand in joy because it is the day of Resurrection and after Pascha (Easter) until Pentecost we do the same. In fact it is forbidden to kneel on these days. It is also forbidden to fast on Saturdays and Sundays. The ascetic way is put aside. Why? I believe to remind us that although we are unworthy sinners God by His Grace has set us free; He has raised us to be sons and no longer servants. This is not something earned but something given freely. Thus, we do not bow the knee as an act of joy and as an testimony that we are saved by grace and we are sons of God; no longer the slaves of God. To bow the knee on Sunday or after Pascha is to insult the grace of God, that has set us free; it is to say that we are saved by works. This also applies to fasting on Saturday, although Lenten Saturdays also forbid meat, eggs and diary products (because of their connection to things sacrificed). We do not fast on Saturdays to again remind us that we partake of the Eucharist on Sunday as a gift of grace and not something we have earned by fasting. We do need to keep the fasts but not on Saturday, so that we are reminded of grace. It is poor teaching to say that one must only partake of the Eucharist if one fasts the day before; this denies grace and makes salvation a matter of works. The form of our prayer matters because it manifests the reality of our lives in Christ, Who was incarnate in the flesh to take us into heaven.
Nevertheless, the Christian path is the way of the Cross and we need to fast and bend the knee in prayer. Without these things we do not participate in the suffering of Christ and unite ourselves with Him. All things must be done in order.
Also, care must be exercise in these matters. Not all bending of the knee is for penance and during ordination such bending of the knee reveals another mystery. There are occasions for other exceptions also but overall the Tradition of the Church is to bend the knee in prayer and to fast but not on Saturday and Sunday as we participate freely in the Grace of God in the joy of the resurrection. Note also, that although it is not formally forbidden to kneel on Saturdays in Holy Tradition, some keep this custom.