Of Excommunicated Persons, how they are to be avoidedThat person which by open denunciation of the Church is rightly cut off from the unity of the Church and excommunicated, ought to be taken of the whole multitude of the faithful as an heathen and publican, until he be openly reconciled by penance and received into the Church by a judge that hath authority thereto.
Archbishop Peter Robinson
In the New Testament we find the words of Jesus Himself, in Matthew 18:15-18
"Moreover if thy brother shall trespass against thee, go and tell him his fault between thee and him alone: if he shall hear thee, thou hast gained thy brother. But if he will not hear thee, then take with thee one or two more, that in the mouth of two or three witnesses every word may be established. And if he shall neglect to hear them, tell it unto the church: but if he neglect to hear the church, let him be unto thee as an heathen man and a publican. Verily I say unto you, Whatsoever ye shall bind on earth shall be bound in heaven: and whatsoever ye shall loose on earth shall be loosed in heaven."
To treat such a person as "a heathen man or a publican" is reflected in the words of St. Paul from the fifth chapter of First Corinthians, "With such an one, no not to eat." The entire chapter is short.
"It is reported commonly that there is fornication among you, and such fornication as is not so much as named among the Gentiles, that one should have his father's wife. And ye are puffed up, and have not rather mourned, that he that hath done this deed might be taken away from among you.For I verily, as absent in body, but present in spirit, have judged already, as though I were present, concerning him that hath so done this deed, In the name of our Lord Jesus Christ, when ye are gathered together, and my spirit, with the power of our Lord Jesus Christ, To deliver such an one unto Satan for the destruction of the flesh, that the spirit may be saved in the day of the Lord Jesus.
1 The distinction to be made is that catechumens are those yet being catechised, that is taught, and have not yet been admitted to Communion.