Question from a non-Catholic: what Catholic Church teaching gives Catholics the authority to declare other members of the Catholic Church are not real Catholics (Catholics in name only)? Thanks for your help; I would like to be able to cite this Catholic Church teaching.
This pretty much sums it up for me. From the Gospel of St. Matthew;
"[16] By their fruits you shall know them. Do men gather grapes of thorns, or figs of thistles? [17] Even so every good tree bringeth forth good fruit, and the evil tree bringeth forth evil fruit. [18] A good tree cannot bring forth evil fruit, neither can an evil tree bring forth good fruit. [19] Every tree that bringeth not forth good fruit, shall be cut down, and shall be cast into the fire. [20] Wherefore by their fruits you shall know them.
[21] Not every one that saith to me, Lord, Lord, shall enter into the kingdom of heaven: but he that doth the will of my Father who is in heaven, he shall enter into the kingdom of heaven. [22] Many will say to me in that day: Lord, Lord, have not we prophesied in thy name, and cast out devils in thy name, and done many miracles in thy name? [23] And then will I profess unto them, I never knew you: depart from me, you that work iniquity. [24] Every one therefore that heareth these my words, and doth them, shall be likened to a wise man that built his house upon a rock, [25] And the rain fell, and the floods came, and the winds blew, and they beat upon that house, and it fell not, for it was founded on a rock."
And this is why it matters. From St. Paul’s 2nd letter to St. Timothy
"[1] I charge thee, before God and Jesus Christ, who shall judge the living and the dead, by his coming, and his kingdom: [2] Preach the word: be instant in season, out of season: reprove, entreat, rebuke in all patience and doctrine. [3] For there shall be a time, when they will not endure sound doctrine; but, according to their own desires, they will heap to themselves teachers, having itching ears: [4] And will indeed turn away their hearing from the truth, but will be turned unto fables. [5] But be thou vigilant, labour in all things, do the work of an evangelist, fulfill thy ministry. Be sober.