When Jesus was on trial, He said, "Everyone on the side of truth listens to Me," to which Pilate flippantly responded, "What is truth?". Many today would echo the same sentiment. But we Christians believe that there is one absolute Truth, and that is the Gospel of Jesus Christ.
We Christians have a responsibility to the truth: a higher responsibility, I would argue, than anyone else. Jesus was known to teach the truth and care little for what men thought. Among a listing of Jesus' qualities it is said that He was "full of grace and truth." We are commanded to worship God in spirit and in truth. We are encouraged to seek only God's glory so that all will know we are truthful. Knowing the real truth about life is what gives us freedom and salvation, and we are commanded to be wise as serpents and discern truth from lies, so that we are not misled by those who are His enemies. Jesus says that Christians are given the Spirit of Truth specifically to aid us in that regard. Jesus prayed that His followers would be made holy by the truth, and we are told that when we delight in God we delight only in the truth. We are called only to do things for truth, and we are warned not to use any falsehood but to speak truthfully to our neighbors.
There are many, many more passages which I could cite, but I think that this suffices to prove my point: we Christians have the key truth of the universe to give to others, and therefore are called to be wise that we neither speak falsehoods nor follow falsehoods. To do so can mislead us away from Christ's message, as well as dilute the reliability of our testimony in front of others.
Let me give you an example. If someone you know constantly buys into every UFO conspiracy theory that they read and talks about it constantly, are you then going to believe them when they tell you that their astrology charts have a key message for your life? Of course not.
Yet that is what many Christians do: we pass around false stories and follow with gullibility anyone who claims to be a fellow Christian--no matter how bizarre or wrong the story that they are selling. So then, when we try to share the Gospel Truth with our neighbor, they reject it: our gullibility in other areas shows us to be uncritical thinkers, and hence why should they believe our story about an ancient God-man who died and lived again?
It is absolutely critical that we are reliable witnesses, lest our testimony about Jesus be thrown out in the court of human opinion. This often manifests itself as hoaxes being shared, as this excellent post demonstrates. But never have I heard of a more egregious example than the tale of Mike Warnke.
Mike Warnke: an example of the danger of hoax-following
Mike Warnke rose to fame in the 1970s and 1980s as a prominent Christian expert in satanism. According to his testimony, Warnke was an orphan and was introduced to Satanism in college. He participated in orgies and drug dealing, as well as occult practices. He claimed to have risen quickly to the rank of 'high priest' of Satanism and oversaw the summoning of demons, casting of magical spells, ritual kidnap and rape, and the murder of some two million people. He then entered the Navy, was saved by Jesus during bootcamp, and became a Christian evangelist and author. Afterwards he claimed to have received two bachelor degrees, two master's degrees, and a PhD. He rose to prominence as a Christian speaker: churches couldn't get enough of his story, particularly Charismatic churches. His fame spread so much that by the 1980s, he was appearing on national news programs. He was immensely popular, and the man and his stories were one of the main reasons that the Satanism scares of the 1980s became widespread.
It was a powerful testimony, I'm sure. Of course, none of it was true.
Warnke was known to be a professing Christian in high school and a member of Campus Crusade for Christ in college (a far cry from Satanism!) As far as I can tell, he never received a single collegiate degree, let alone the 5 he claimed. His own books contradict each other in their war stories (some saying he was wounded twice, others five times). His claim of 2,000,000 ritual murders per year is patently disprovable: this is like the entire state of Arkansas' population disappearing each year without anyone noticing.
His lifestyle certainly didn't bear out scrutiny, either. He cheated on his first wife at Trinity Bible college and later divorced his first wife to marry his mistress. Then he cheated on his mistress while on a speaking/comedy/ministry tour, and beat his wife: he threatened that if she went to the hospital he would kill her. His second wife fled to Florida to live in secret. He married his second mistress. It should come as no shock that they too would later divorce when he cheated with yet another woman. His record sales alone earned him more than $7 million, not to mention book sales and other such income; and yet, some years he gave as little as $900 to charity from these albums which purported to raise money for charity.
This man became a multimillionaire Christian speaker and one of the faces of the faith. Churches gobbled his story up.
And yet it was 18 years before a Christian organization ever decided to look into his story.
Cornerstone Magazine began investigating Warnke in 1991, when they learned that a child he claimed to have sacrificed as a Satanist had actually never existed. They interviewed friends and family and saw tax returns, finding that he was in fact a very regular and unnoteworthy college student who dropped out and joined the military, as many did at the time. His claims of palling around with Charles Manson were proved untrue, as Manson was in jail at the time that Warnke claims they were co-Satanist priests. They proved that the timelines he claims to have done things were so contradictory that his entire "multi-year" rise to priesthood and dominance of Satanism had to have happened within a mere nine months. They found that his claim of leading 1,500 fellow Satanists was provably untrue, and even Warnke admitted that there were only 13 (of whom, conveniently, 5 he forgot the whereabouts to and the other 8 were dead). Further investigation showed that while Warkne was paying himself a salary of nearly $1 million, he was claiming his ministry to be destitute and in need of fundraising. Eventually even his publisher and record company dropped him, as more and more evidence began to come out. Indeed, virtually every verifiable fact he gave turned out to be completely false.
The worst part of the story? After a decade of lying out of the spotlight, Warnke has begun a comeback in the 2000s in small churches, claiming that his story was only "slightly exaggerated" and that he was the target of mainstream Christians.
My sad prediction: he will find audiences. I have sat before in Christian churches listening to someone's testimony and my "falsehood" detector was going off like crazy, while everyone around just ate up the amazing story of how Jesus saved this person from a hellish lifestyle. A few minutes' research told me the speaker was full of it, and that turned out to be the truth (as we all found out later). The sad truth is that for many Christians, if someone includes the phrase, "But Jesus saved me from that lifestyle," then everything else the speaker said gets a pass--no matter how absurd.
We as Christians have to be better than this. Do not pass around that Obama hoax email, or repeat a conspiracy theory, or follow the Mike Warnkes of the world, or abide by silly superstitions about the number 13 or walking under a ladder, or just grant a "I will believe you" card to anyone who uses the name of Jesus from a pulpit. This is not what Jesus taught us, and this is not what the Spirit within you desires. Believing lies is not love, and there is nothing unloving about praying and researching to be sure you are being told truth.
To follow falsehood--and worse, to repeat it to others--makes your witness lose all credibility. How can you be a keeper of God's truth when you are so gullible as to believe any lie thrown at you by a professed Christian?
And not only is your credibility shot, but you yourself may be led astray by these "sheep in wolves' clothing." Jesus talked about this constantly (see Scripture references below): people will use the name of Christ to try and lead astray true believers. And He told us that our task was to protect ourselves from these falsehoods!
Dear Christian, do not let yourself be used by enemies of the One True God, or by con artists seeking riches and women. We live in the information age, and we have no excuse to fall for such things: learn to use Google and Snopes and basic critical thinking, lest peddlers of lies ruin your witness for God.
 John 8:37-38
 Matt 22:16, Mark 12:14, Luk 20:21
 John 1:14-17
 John 4:23-24
 John 7:18
 John 8:32
 Matt 10:16
 Matt 24:23-27
 Acts 29:29-31
 John 15:26
 John 17:6-18
 1Cor 13:6
 2Cor 13:8
 Eph 4:25