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Most people who claim to be Christians do not obey Jesus and therefore must not really believe who He is and are therefore not His true "sheep".

Jesus said, "But because you are not My sheep, you refuse to believe. My sheep listen to My voice; I know them, and they follow Me. I give them eternal life, and they will never perish. No one can snatch them out of My hand.…"

But most people who claim to be sheep are in for a surprise. Two more Jesus quotes:

"I know your deeds, that you are neither cold nor hot. I wish you were either one or the other! So, because you are lukewarm—neither hot nor cold—I am about to spit you out of my mouth."

"Many will say to Me on that day, ‘Lord, Lord, did we not prophesy in Your name, and in Your name drive out demons and perform many miracles?’ Then I will tell them plainly, ‘I never knew you; depart from Me, you workers of lawlessness.’"

So feel free to criticize false Christians. As you can see, Jesus also criticizes them.