John 13:4-10:, 8 Peter said to Him, “You shall never wash my feet!” Jesus answered him, “If I do not wash you, you have no part with Me.” Simon Peter said to Him, “Lord, not my feet only, but also my hands and my head “10 Jesus said to him, “He who is bathed needs only to wash his feet, but is completely clean; and you are clean, but not all of you
Jesus washed the disciple’s feet but then as He got to Peter, Peter objected. I think that we would have all likely objected until we understood why. This was about submitting to Jesus will whether Peter and the rest understood it or not.
This action signified the continuous work in salvation termed as sanctification. Jesus wanted to remind them that they were already clean. And though their feet were dirty, He was demonstrating the continuous cleansing, not for regeneration but for sanctification. Salvation is a one-time act of justification by faith, but the lifelong process of sanctification is one of continuous washing from the stain of sin we experience as we walk through the dusty world, and commission to serve one another (Eph 5). This is the Comfort believers have, they are already clean in regeneration, and their feet are cleaned in sanctification.