John Piper has warned Christians not to live a "double life" in the wake of the Ravi Zacharias scandal.

The Desiring God founder admitted he had been "slow to speak" on the issue because of how "horrible" it is to "publicly assess and criticize" someone who was a a husband, father and friend. 

But speaking on the Ask Pastor John podcast, he said it was "right" for people to be asking him about his view on the scandal, particularly where it concerns people who were deeply influenced or converted by his ministry. 

Piper cited three people in the Bible - Judas, Demas and Hymenaeus - who "for a season, spoke the truth in useful ways, and then made shipwreck of their lives". 

Judas, he said, had presumably been preaching the gospel and performing miracles along with the other disciples, all the while being a "son of perdition". 

"And lest anyone think that a phony apostle can't do miracles, remember the words of Jesus in Matthew 7:22–23," Piper said. 

In the passage cited by Piper, Jesus denies knowing those who cast out demons in his name because they were "workers of lawlessness". 

"And those works of lawlessness would, of course, include things like pervasive deception; greedy, lavish use of ministry funds; harmful manipulation of other people for your own private pleasures; adulterous dalliances; continually making provision for the flesh against the explicit command of the apostle in Romans 13:13–14," Piper explained. 

Demas, too, was a "trusted" gospel partner until he deserted Paul and went to Thessalonica because he was "in love with this present age".

When his "true colours were revealed", it was shown that Demas really loved "only what this age was offering him through religious work: things like association with notable people, access to money, experiences of power, accolades for eloquence, commendations for courage," Piper said. 

Of Hymenaeus, Piper said he and Alexander started out with faith but eventually "found ways to dull their conscience, until their conscience was so seared that they could justify behaviors that were simply appalling, even to the point where Paul said they made 'shipwreck of their faith.'"

"A double life, lived contrary to the Christian conscience, is a shipwreck about to happen," Piper said. 

Speaking specifically about Zacharias, Piper criticized the late apologist's "manipulation of people", which he said was a lesson to everyone about "the need for tethered sympathy", which he defined as sympathy that is "tethered to the truth." 

"How did Ravi manipulate people into sinfully sending him nude pictures? How did he manipulate people into sinfully providing him with sexual stimulation? He did it by demanding untethered sympathy," Piper said.

"He portrayed himself as an embattled, burdened, wounded warrior in the righteous cause of the gospel. And ironically, he turned his position of power into a form of neediness and woundedness, and then he tried to coerce untethered sympathy under the guise of calling for 'kingdom therapy for the wounded warrior.'"

Piper also warned against lavish living.

"The amassing of money and the pursuit of lavish lifestyles in ministry are the alarm bells of the love of this age," he said. 

He ended by encouraging those who came to Christ or were influenced through Zacharias' ministry to look at Christ and not abandon their faith. 

"Don't let the imperfections and failures of men turn you away from the perfections and the triumphs of Christ, who will never, never fail you," he said.