You have no idea what you're talking about. You have a bad attitude about ecumenism because that's what your Protestant mentors have brainwashed you to believe. I go to several different Churches but I will never call myself a Protestant and your reply is one reason for it.
Christ and several others taught and prayed for unity, But you Protestant's, esp. the Fundamentalist Baptist, have badmouthed unity so much that you've all been deceived!
I'm really surprised how easily people take scripture out of context. I didn't read all the replies on this thread but I have to wonder if anybody caught that. The topic is a good one but the verse is completely mis-applied.
Lawlessness is a simple thing to understand. In nearly every context that the word is used in it never refers to Christian's or their walk with Christ. Lawlessness isn't being lukewarm or even one who is backslidden. Lawlessness is an atribute of the wicked!
Lawlessness is...
1) the condition of without law
a) because ignorant of it
because of violating it
2)
Iniquity:
This is what Vines say's...
lit., "lawlessness" (a, negative, nomos, "law"), is used in a way which indicates the meaning as being lawlessness or wickedness. Its usual rendering in the NT is "iniquity," which lit. means unrighteousness. It occurs very frequently in the Sept., especially in the Psalms, where it is found about 70 times. It is used
(a) of iniquity in general, Mat 7:23; 13:41; 23:28; 24:12; Rom 6:19 (twice); 2Cr 6:14, RV, "iniquity" (AV, "unrighteousness"); 2Th 2:3, in some mss.; the AV and RV follow those which have hamartia, "(man of) sin;" 2Th 2:7, RV, "lawlessness" (AV, "iniquity"); Tts 2:14;

r 1:9; 1Jo 3:4 (twice), RV, "(doeth) . . . lawlessness" and "lawlessness" (AV, "transgresseth the law" and "trangression of the law");
(in the plural, of acts or manifestations of lawlessness, Rom 4:7;

r 10:17 (some inferior mss. have it in

r 8:12, for the word hamartia).
See LAWLESSNESS, TRANSGRESSION, UNRIGHTEOUSNESS.
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The Arab's and Muslim's, whether in the Mid-East or in Africa, are the most lawless people in the world. Mathew 24:12 has absolutely nothing to do with Christian's. It often does have something to do with the most lawless and prophesied evil religion of the last day's.......ISLAM!