Based on history, the act of genuflecting on one knee emanates from court etiquette and was also done while in the presence of a medieval king or noble. It was a sign of respect and also a pledge of service. Over time, Christians adopted this custom, and it became fully adopted into the liturgy of the Roman Rite by the 16th century.
Knowingly to the Jews and Christians, God has always been a king who is rich in mercy and boundless in love. In order to give honor to that "King of Love," Christians thought it fitting to pay homage and honor to him by genuflecting every time they enter his court.
Genuflection symbolizes our heart bowing before the Lord who is substantially and really present in the Eucharist. As Catholics, we believe that Jesus is truly present, Body, Blood, soul and divinity in the Holy Eucharist and so when we genuflect, we do so because we are in the presence of God. The Catechism of the Catholic Church (CCC 1378) affirms this teaching, "In the liturgy of the Mass we express our faith in the real presence of Christ under the species of bread and wine by, among other ways, genuflecting or bowing deeply as a sign of adoration of the Lord". St. Ambrose said, "The knee is made flexible by which the offense of the Lord is mitigated, wrath appeased, grace called forth," and Alcuin later added, "By such a posture of the body we show forth our humbleness of heart."
Following the same line of thought, kneeling also holds a special place in fostering a proper reverence. Going back to our Lord's time, the Jewish people often stood while praying; however, when the occasion was solemn, the petition urgent, or the prayer was offered with great fervor, then the person humbly knelt before his God to pray. For instance, when Jesus prayed in the Garden of Gethsemane, the gospel reads, He "went down on His knees and prayed…" (Luke 22:41).
Finally, we do these bodily actions because both our religion and our prayer, demands bodily expression. Because Jesus, the Risen One, gives himself in the Body, therefore, we have to respond in soul and body all the spiritual possibilities of our body are necessarily included in celebrating the Eucharist be it singing, speaking, keeping silence, sitting, standing and kneeling.
Fr. Antonius David Tristianto, O.Carm.