At the instant of salvation we are “bathed all over,” our sins are removed, we receive a new heart, and we are completely forgiven (Revelation 1:5; Titus 3:3-7; and 1 Corinthians 6:9-11). Jesus promises us that through His death he will “remember our sins and iniquities no more” (Hebrews 10:17). But, going through life in such a sin filled world leads to regular defilements. But as one united to Christ we do not need to get “saved again”, we just need to have that specific stain, sin, or defilement cleansed away. That is the essence of 1 John 1:9 where we see that if we are constantly confessing our sins “washing a specific part” (that is the tense of the first verb) God is faithful and just to already once-and-for-all to have cleansed us “bathed all over” (that is the tense of the second verb). What a comfort for us who slog through this muddy world that we don’t get unsaved when we sin; but we can’t enjoy the delights of our salvation as long as we carry the mud of the world upon our redeemed hearts. Repent and confess and be washed.
That is why it is so important that we “keep our feet clean”. When we are defiled, we lose fellowship with our Lord. That is what Jesus was saying to Peter when He said, “If I wash thee not, thou hast no part with Me” (John 13:8).
Christ's word translated “part” was meros, which means “participation, having a share in someone or something.” Salvation was God “bathing us all over”. Then God united us to Jesus in a settled relationship that cannot change. We see this permanence in the verb wash in John 13:10; because it is in the perfect tense it means that the washing was settled once and for all. Fellowship with Christ is tied to whether we keep ourselves “unspotted from the world” (James 1:27). If we permit un-forsaken and un-confessed sin in our hearts and minds, our walk with the Lord gets obstructed; that is why we need to have our feet washed.
Taken from "Servants of God Stay Pure - Love on Its Knees" by Discover the Book Ministries.