The Blood of Jesus (1 John 1:7) cleanses us from all sin.
Why did Jesus (John 13:5) wash the disciple’s feet? To make their feet clean! We are (John 13:14-15) to follow His example. Foot washing is a type, an example of meeting one another’s needs to make them clean. If a fellow-Christian (Galatians 6:1) is overtaken by sin, we are not to judge them and shutter them out but to restore them to be clean in God’s sight and restored to the fellowship of believers. We will be blessed (John 13:17) as we obey the Word of God.
To choose to obey in everything (Psalms 119:103-104) through your precepts I get understanding, therefore I hate every false way. How sweet are your words to my taste. Sweeter than honey to my mouth. The Word of God, the living Word of Eternal God, continually fuels, increases our spiritual appetite for more. Our constant desire to be clean before God is because God has commanded us (Leviticus 11:44, 1 Peter 1:16) to be holy because the Lord our God is holy.
The secret of the Lord (Psalms 25:14) is with them that fear Him. This does not mean to be afraid of God but in loyal, loving worship we so adore Him that we fear to grieve Him. To have such a close intimate relationship with God that He reveals the secrets of His heart to us. That is a relationship we must pursue to be so close to the Lord that not even a shadow can come between us.
God has formed us (Isaiah 43:21) for Himself. Growing old is automatic but (Ephesians 4:13) growing up in Christ Jesus requires separation, obedience, surrender, commitment and self-denying discipline. Are we living (Ephesians 1:12) for the praise of His glory and fulfilling the purpose for which God created us, redeemed us and placed us where we are? The people who know their God (Daniel 11:32) will be strong and do exploits.
The secret things (Deuteronomy 29:29) belong to God and as we are growing deeper in intimacy with Him, He reveals to us His secrets which are hidden from the disobedient and enables us to obey Him. Our desire increases more and more for God and will constantly increase.
We will always be satisfied with God but never satisfied that we have enough of God on His precious Highway of Holiness. Our motive for everything we think say and do, will be (1 Corinthians 10:31) to glorify God.
That is why we wash feet.