What we do with our bodies matters. Our physical gestures express our inward attitudes, and contribute toward establishing and fostering them. So, just as we lift holy hands to the Lord, and stand in reverence for God’s Word when it is read, we also kneel in humble confession. We want to be a humble and penitent people before God. We humble ourselves in our posture, kneeling before God.
When the Scriptures tell of God’s people praying to Him, they are usually kneeling. Solomon, Daniel, Jesus in Gethsemane, and the New Testament church are just a few examples, besides the Psalmist calling us to worship saying, "Let us worship and bow down; let us kneel before the LORD our Maker" - Ps 95:6.
This reminds us to confess our sins