Jehovah's Witnesses often use this passage to prove to others that your SPIRITUAL brother is to be shunned if he does not listen to you. If your brother sins against you, go and show him his fault, just between the two of you. If he listens to you, you have won your brother over. But if he will not listen, take one or two others along, so that 'every matter may be established by the testimony of two or three witnesses.' If he refuses to listen to them, tell it to the church; and if he refuses to listen even to the church, treat him as you would a pagan or a tax collector. Source: Matthew 18:15-17 If the term brother has multiple meanings (like this one-"those united in a general cause and having similar aims and purposes") then why do the Jehovah's Witnesses only choose one meaning (SPIRITUAL BROTHER) to the verse mentioned above that is, in the Christian congregation members enjoy a common spiritual relationship analogous to that of brothers.
Insight Volume 1 pg 369
“Brother” is also applied to those united in a general cause and having similar aims and purposes. For example, King Hiram of Tyre called King Solomon his brother, not simply because he was an equal in rank and position but also perhaps because of mutual interests in supplying timbers and other things for the temple. (1Ki 9:13; 5:1-12) “Look! How good and how pleasant it is for brothers to dwell together in unity!” David wrote, implying that it is not blood relations alone that make for peace and unity between fleshly brothers. (Ps 133:1) In fact, mutual affection and interest, not common parentage, prompted David to call Jonathan his brother. (2Sa 1:26) Companions having similar natures and dispositions, even when such are bad, are properly called brothers.—Pr 18:9.
In Matthew 18:21 Then Peter came up and said to him: “Lord, how many times is my brother to sin against me and am I to forgive him? Up to seven times?” 22 Jesus said to him: “I say to you, not, Up to seven times, but, Up to seventy-seven times.
Seventy-seven, a repetition of seven in a number, was equivalent to saying “indefinitely” or “without limit.” Jesus counsels Christians to forgive their brothers to that extent. (Mt 18:21, 22)
So if Jesus says to forgive seventy-seven times meaning indefinitly and the word "brother" (Hebrew, 'ach, and in Greek, a·del·phos) knowing it has multiple meanings, does that change the whole context of NOT shunning your NON SPIRITUAL brother and forgiving him indefinitly? Again, brother has multiple meanings one being, in this example "those united in a general cause and having similar aims and purposes" BUT not necessarily having a spiritual connection.
My point is: Shouldn't this just mean that we are to forgive anyone (brother-mankind) who goes against us and not just your spiritual brother?