That highlighted comment is often tough to know. Many people are sincere, but sincerely wrong, because their beliefs don't line up with Scriptures. There's also the posers who might say what they think you want to hear in order to get who they want. They aren't saved and you don't know that up front. I can give a couple examples of that from my past.
One extreme example was Maria who was demon possessed. I learned that in the middle of the day on campus between the Chemistry building and the main library. The demoniac in the gospels was a good description of what I saw that day. That started out scarry. I could have lost my life at the hands of her that day. She admitted to not being saved shortly after at the breakup. All of that was wasted time, emotions, work and money that would have been better used for God's purposes.
Related to that point is a passage from 2 Peter 2
"But there were
false prophets also among the people, even as there shall be false teachers among you, who privily shall bring in damnable heresies, even denying the Lord that bought them, and bring upon themselves swift destruction.
2 And many shall follow their pernicious ways; by reason of whom the way of truth shall be evil spoken of....For it had been better for them not to have known the way of righteousness, than, after they have known it, to turn from the holy commandment delivered unto them.
22 But it is happened unto them according to the true proverb, The dog is turned to his own vomit again; and the sow that was washed to her wallowing in the mire."
This brings me to the Josh Harris book that I read. I agreed with his concepts of purity and establishing proper habits to maintain that. There was a lot of wisdom in the book for a guy just out of highschool...20.
It really wasn't something that you had to be saved to understand though. That was his biggest problem. He was trusting in his morality and repentance from sins to be saved.
Even though he went on to be hired by an evangelical mega church, that didn't make him a born again Christian. I wondered why a pastor goes to some liberal theological seminary after landing that ministry. Then he renounces what he claimed to believe about the Bible and the Lord it describes. I checked out his church's doctrines on salvation and it's a hard core works method.
"NOT by works of righteousness which we have done, but according to His mercy He saved us."
Titus 3:5
Josh did not receive God's mercy, because he went about to establish his own righteousness. As a pastor, he was a false prophet leading many astray to a firey destiny. As a false prophet, he eventually became reprobate. He went down the slippery slope of too many pastors.
I've seen that happen more than once too.
I Timothy 4:1-3