Why do we receive at an altar rail?
The altar rail is on the surface a practical aspect of Church architecture. It acts as the dividing point between the sanctuary and the rest of the Church. Even in ancient times, it kept people from accidentally entering the sanctuary or crowding the ministers of the altar. It also represents the division between the different roles of those who worship at Mass. The priest and the sacred ministers serve at the altar while the laity participate with their prayers and devotion during Mass. As the laity approach the altar to receive Holy Communion, they come to the altar rail which then acts as an extension of the altar itself because it is there that they receive. Just as one can only receive a foretaste of heaven in this life, one can only approach to the edge of the sanctuary.