"Enter ye in at the strait gate: for wide is the gate, and broad is the way, that leadeth to destruction, and many there be which go in thereat:
Because strait is the gate, and narrow is the way, which leadeth unto life, and few there be that find it." Matt 7:13-14
How many are few? Could it be only 8 [like Noah's family]a long with a bunch of clean and unclean animals? Or could it be just 2 out of 600,000 who came out of Egypt?
But those are the ones who found the strait and narrow gate. Your question relates to the OP, which seemingly relates to the ones, who among Christians, do not... Hmmm?
My wife does a very good job of picking out the good fruit at the market... me, not so good!
How good is anyone at sorting through the general labeled Christian population as fruit inspectors? Not good at all... if they are people, we have never meet nor interacted with at all!
There are a whole lot of people walking around that Jesus would name as dead people. Those would not really be followers of Christ, would they?
Many people, I believe, fail to recognize zombies when they see them. God recognizes who is and who is not a zombie!
Most all of my life I was attending places called church. I stopped doing that, three times, since leaving active Catholicism [1) 11 years, 2) 10 years] and 3) beginning in October of 2018.
Aside from those stoppages how often was I gathering with others in "Jesus Name"? How often are the socializers actually in His Name? Are some of them really zombies? If they never are "in Jesus Name", one might seriously consider whether or not they are really "Christians". I guess that would depend on your definition of that word, Christian.
Tares among the wheat... but who is a harvester given the eyes to know them when he sees them? Does anyone ever effectively treat a grain of wheat like a tare? God makes no mistakes, but do not children of God still make some mistakes?
How many of the other 11 disciples of Jesus recognized Judas as that one before he met them in the garden to give Jesus a kiss of betrayal? Who needed to recognize him then?
Fortunately for all of us, neither you nor I get to make that final judgement on all of them. Are we qualified? I am not!
Again... the judgement only belongs to God because He alone knows all of the facts about everybody and is able to judge everybody fairly.
Jesus, I believe, described how it is to be done here:
"But he that knew not, and did commit things worthy of stripes, shall be beaten with few stripes. For unto whomsoever much is given, of him shall be much required: and to whom men have committed much, of him they will ask the more." Luke 12:48
What will we have done at the end of our cource with all that has been given to us? Time, intelligence, charity, faith, material goods or abject poverty, secular or religious education, skills, opportunities, etc.?