If they reject the gospel, then the Lord allows the Devil to sort of blind their eyes! (Maria: It says, "In whom the god of this World hath blinded the minds of them which believe not, lest the light of the glorious Gospel of Christ, Who is the image of God, should shine unto them.") (2Cor.4:4)
Having rejected the Gospel, the Lord then allows the Devil to blind them and give them strong delusion that they might believe a lie, that they might be damned. (2Th.2:10-12) When they reject it, they've rejected the Holy Spirit and committed the unpardonable sin in rejecting Jesus Christ. (Mat.12:31,32)
(Maria: So even though their counsel seems good and seems pretty much according to...) A lot of the Devil's religions are very good.--They can be very good and just lack one thing: Receiving Christ as Saviour. (Maria: You said about this woman's book that it might not be possible to tell whether her source was actually the Devil or the Lord unless you knew whether she believed in Jesus, because her counsel sounds good about everything.) It can sound mostly good and yet doubt the Lord!
The Devil preaches a lot of truth and a lot of good, just so that people will steer clear of Jesus! He even preaches God, as long as they don't mention Jesus.--Like the Jews. Even the Muslims come so close.--They receive Jesus as a great Prophet and Teacher and give Him more credit than some of the Jews will give Him, but they won't accept that He's the Son of God or the Saviour.
So the Devil preaches a lot of truth and a lot of good. He even quoted Scriptures to Jesus! He's a great quoter of Scriptures! He always uses half-truths, and that makes his deceit all the more clever. What he promises is half-good and half-true, but there's always a hidden lie and hidden evil in it. That's why Jesus is the test: "Try the spirits!--Every spirit that confesses that Jesus Christ is come in the flesh is of God." 1 John.4:1-3)
Most religions are counterfeits.--They're not exact opposites, they're deceptions.--The Devil was an angel of light! So you don't know until you ask them, "What think ye of Jesus Who is called Christ?" (Mat.22:42) That's the corker, that's the question!
So, "What think ye of Jesus?"--I've asked a lot of people that who wanted to argue religion. I'd say, "Tell me what you think of Jesus! Just tell me what you think about Jesus! There's no use arguing about anything else at all. You just need to know whether they receive Jesus, accept Jesus and believe in Jesus or not! Sometimes they can believe in Jesus and have all kinds of crazy haywire doctrines on Bible Prophecy and a lot of other things, like a lot of Christians do, but what difference does that make?
The only thing we have to worry about is whether they're saved or not, whether they've received Jesus! That's the crux of the whole thing, whether they want Jesus or not. If they say they believe in Jesus, I don't care whether they're Catholics, Jehovah's Witnesses, Seventh-day Adventists, Mormons or nothing at all!--If they really believe in Jesus as the Son of God, their Saviour, and they receive Him as such, then okay!
"For I determined not to know anything among you, save Jesus Christ, and Him crucified." "Neither is there Salvation in any other: for there is none other name under Heaven given among men, whereby we must be saved." (1Cor.2:2 ; Ac.4:12 .)