In the United States, our practice is to kneel (if we are able) from the end of the “Holy, Holy” until after the Great Amen at the end of the Eucharistic Prayer. We also kneel after the “Lamb of God” until the time for Holy Communion.
Kneeling is a sign of humility before God who is humble enough to strip off the glory of divinity, and take on our human nature, like us in all ways but sin. It is part of the culture of Christians to kneel.
Kneeling can also add to the intensity of our pleading to God in prayer, or express our adoration of Jesus, the Son of God, who becomes really present when the bread and wine are consecrated.
Some people kneel as if to pray when they return to their pew after receiving the Eucharist. But as no specific posture is required, people may also either stand or sit.
This is part of a series on how to worship at Holy Mass by Archbishop Jackels. The name comes from the "4 H's" of the 2nd Mission Priority: Enhancing the Sunday assembly for Holy Mass. This series was published between February and December of 2017.