The Lord Jesus Christ instructed, “He who is bathed needs only to wash his feet, but is completely clean” (Jn 13:10).
In Greco-Roman times, it was customary to wash one’s feet after bathing, for even after a person had bathed (e.g. at a public bath), the feet would get dirty from the dust stirred up during the walk home. Footwashing was necessary to be completely clean. So even though baptism washes away our sins, footwashing prepares our feet to walk in righteousness and purity to reach our heavenly home.