The following is excerpted from Customs of Primitive Churches by Morgan Edwards (Philadelphia, PA: 1768, p. 93), Thanks to Chris Hanna of Hudsonville, Michigan for providing me a pdf version of Customs of Primitive Churches, Or, A Set of Propositions Relative to the Name, Materials, Constitution, Power, Officers, Ordinances, Rites, Business, Worship, Discipline, Government, &c. of a Church.
XXXII. Washing feet is a rite of divine original and perpetual obligation. The ends of it are, to oblige christians to be beneficently condescending one to another; and to signify to them a cleaning from the sins they are liable to after baptism. The performer of the rite is any christian. The place is, at home. The time, once a year, at least. The attendants of the rite are, supper or love feast etc. The requisites are, water, bason, towel, and a form of words expressive of the ends of the rite.
1. That washing feet, considered as a christian rite, is of divine original, appears from John xiii. 1- where we have an account of its institution.
2. That it is of perpetual obligation appears (1) From the command which Christ grounds on his example; and the blessedness he pronounceth to the observers Joh. xiii. 15, 17. (2) From the practice of the first christians 1 Tim. v. 17. (3) From the ends proposed by it, which always abide.
3. The ends of the rite are, (1) To inculcate to christians a beneficent humility, condescension and love; and to condemn the contrary. So Christ explains the matter. John xiii. 10, 16. (2) To be a sign to the party washed of his cleansing from sing. It signifies a washing, without which we can have no part in Christ Jesus, v. 8, and a washing consequent upon some other of like signification, viz. baptism. Acts xxii. 16; our baptism signifies a washing from sin committed before it. 2 Pet 1. 9. Some of those sins may be repeated; or if they be not, there is no man that liveth and sinneth not; yet baptism is not to be repeated; opportunely therefore doth this rite frequently come in to encourage hope of a cleansing from sins committed after baptism.
4. The performer of the rite is, any christian, even a female. 1 Tim. v. 10.
5. For the time allotted for this rite we have no rule, except take either example or convenience for rules. If the former, we have the example of Christ; who celebrated it two days before he suffered, compare Joh. xiii. 1 with Mat xxvi. 2, which day was the first of April, for he died the third. This rule will make it an annual thing only. But expediency requires it should be observed oftener, as the first christians most probably did. 1 Tim. v. 10.
6. An example of the manner in which it has been performed occurs under prop. xxxi.