The motion before entering a pew is called genuflection. One bends the right knee to the floor, while bowing the head in the direction of the Tabernacle and crossing oneself. This is to adore Christ, who is in the Tabernacle in the reserved Host.
The Ceremonial of Bishops states it beautifully and simply (CB 69).
“A genuflection, made by bending only the right knee to the ground, signifies adoration, and is therefore reserved for the Blessed Sacrament, whether exposed or reserved in the tabernacle…”
Inaestimabile Donum also reflects on this beautiful expression and the related disposition of the heart (ID 26)
“This venerable practice of genuflecting before the Blessed Sacrament, whether enclosed in the tabernacle or publicly exposed, as a sign of adoration, is to be maintained. This act requires that it be performed in a recollected way. In order that the heart may bow before God in profound reverence, the genuflection must be neither hurried nor careless.” (ID 26)
Before and after Mass – It is the norm to genuflect when passing before the Blessed Sacrament in the tabernacle. The Ceremonial of Bishops (CB 71) says,
“No one who enters a Church should fail to adore the Blessed Sacrament either by visiting the Blessed Sacrament chapel or at least by Genuflecting. Similarly those who pass before the Blessed sacrament genuflect, except when they are walking in procession.”
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After genuflecting, we enter the pew and kneel to pray to prepare ourselves for the reception of Holy Communion. It is a posture of a humble penitent. We examine our conscience (something we should be doing every evening before bed) for sins, both those of comission and omission. If they are mortal, one should refrain from the Eucharist. You can use your own words, bringing to God something you have been having a problem with perhaps, or you can recite one of the prayers in the missal for use in preparing one’s soul for Mass. I like the
Prayer of St. Ambrose. I found it particularly helpful when I was going through a period of great dryness and had no words of my own.
We kneel at the Consecration to Adore Christ who is manifest upon the altar, as His eternal sacrifice is made present, and the bread and wine become the Body and Blood of Jesus. and remain kneeling in Adoration of Christ’s Real Presence until the reserved Hosts are placed in the Tabernacle and it is closed. During this time. you can pray using your own words or one of the prayers provided in the missal for that purpose. The kneeling is not so much of a prayer posture as that of our submission to God. I think that if we had any true inkling of what the Real Presence was, we would be flat on our faces before the Glory of God.
When you hear the priest say, “Let us pray”, we will all stand, because standing is the traditional posture of prayer.
Kneeling in prayer at other times is a just a personal preference but at Mass, it has a special meaning.