he who is bathed (v. 10) — the new birth, regeneration by water (the Word) and the Spirit (Titus 3:5). Once accomplished, it cannot be repeated.
needs only to wash his feet (v. 10) — referring to the believer’s walk which needs the cleansing of the Word (Ephesians 5:25-26). But the believer needs no further washing because, before God, he is spotless.
The first “washing” in verse 10 is from the Greek word for “bathed.” The second washing is from the Greek word for “cleaning the extremities.”
This same distinction was plainly marked in the Old Testament. When Aaron and his sons were consecrated, they were bathed all over (Exodus 29:4; Leviticus 8:6); but at the laver it was only their hands and feet which were daily cleaned (Exodus 30:19-21). — Pink, page 308