Matthew 24:11 (AMP)
11 And many false prophets will rise up and deceive and lead many into error.
Matthew 15:9 (ASV)
9 But in vain do they worship me, Teaching as their doctrines the precepts of men.
Matthew 24:5 (ASV)
5 For many shall come in my name, saying, I am the Christ; and shall lead many astray.
It is very easy to decieve religous people because they are not interested in studying the Bible.....they more willing to listen to and believe what ever some religious figure head tells them. Jesus said His sheep (followers) listen to Him and follow Him.
John 10:27 (ASV)
27 My sheep hear my voice, and I know them, and they follow me:
It is impossible to deceive them because they will flee from the deceiver just as a sheep would flee from a stranger.
John 10:1-5 (ASV)
1 Verily, verily, I say unto you, He that entereth not by the door into the fold of the sheep, but climbeth up some other way, the same is a thief and a robber.
2 But he that entereth in by the door is the shepherd of the sheep.
3 To him the porter openeth; and the sheep hear his voice: and he calleth his own sheep by name, and leadeth them out.
4 When he hath put forth all his own, he goeth before them, and the sheep follow him: for they know his voice.
5 And a stranger will they not follow, but will flee from him: for they know not the voice of strangers.
Throughout Jesus' ministry He told parables and the parable of the wheat and the tare was one of them.
Matthew 13:24-30 (AMP)
24 Another parable He set forth before them, saying, The kingdom of heaven is like a man who sowed good seed in his field.
25 But while he was sleeping, his enemy came and sowed also darnel (weeds resembling wheat) among the wheat, and went on his way.
26 So when the plants sprouted and formed grain, the darnel (weeds) appeared also.
27 And the servants of the owner came to him and said, Sir, did you not sow good seed in your field? Then how does it have darnel shoots in it?
28 He replied to them, An enemy has done this. The servants said to him, Then do you want us to go and weed them out?
29 But he said, No, lest in gathering the wild wheat (weeds resembling wheat), you root up the [true] wheat along with it.
30 Let them grow together until the harvest; and at harvest time I will say to the reapers, Gather the darnel first and bind it in bundles to be burned, but gather the wheat into my granary.
In the same way most of us are unable to tell the difference between a wheat and a tare, so it is that most people cannot always tell the difference between a true Christian and one that is not.......they assume that just because a group or a people come under the banner of Christianity it automatically mean that they are whom they claim they say they are.
But Jesus said we know someone by what they do.
Matthew 7:15-20 (ASV)
15 Beware of false prophets, who come to you in sheep's clothing, but inwardly are ravening wolves.
16 By their fruits ye shall know them. Do men gather grapes of thorns, or figs of thistles?
17 Even so every good tree bringeth forth good fruit; but the corrupt tree bringeth forth evil fruit.
18 A good tree cannot bring forth evil fruit, neither can a corrupt tree bring forth good fruit.
19 Every tree that bringeth not forth good fruit is hewn down, and cast into the fire.
20 Therefore by their fruits ye shall know them.