Prostrations and kneeling are most often associated with penance, submission, and obeisance. This is why we practice them with such routine and fervor during the Lenten seasons: those specific occasions to which we are directed to meditate upon and acknowledge our sinfulness and to seek reconciliation with God through repentance (Confession). 

However, due to the extremely joyous nature of Paschaltide, and in remembrance of Christ’s saving Passion and Crucifixion for the remission of our sins, we celebrate with exuberance this period in between Great and Holy Pascha and the Feast of Pentecost by not kneeling during prayer (in church or at home). This is in accordance with the twentieth canon of the First Ecumenical Council (325 A.D.), which forbids kneeling on Sundays and the fifty days between Pascha and Pentecost.