Can anyone speculate what the delusion that God sends and the lie that is believed is, quoted in this verse: "and for this cause, God shall send them strong delusion, that they should believe a lie...that they all might be damned who believed not the truth but had pleasure in unrighteousness."
The clue is the word I bolded and made red.
"un-right-ness" = wrong-ness; lawlessness; sin.
The person this passage is
connected to is the man of "law-less-ness" AND connected to
believers falling away from the original faith...because they take pleasure in sin.
The Greek word used is "Adikia" meaning (properly) "the opposite of justice" and is used to mean "evil-doers" and "wickedness". When we talk about righteousness, lawlessness, evil, etc., we're referring to God's law.
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The strong delusion is that God's Law is done away; that a believer in Messiah doesn't need to try to obey God's Commandments because the believer can't possibly do so (even though they've been saved from bondage to sin by Messiah's blood and received Messiah's gifts of Grace and Holy Spirit and faith as well as access to the throne for forgiveness) and because Messiah has been obedient for us.
If one challenges the idea that the law is done away you'll be met with anger and venom from brothers and sisters.
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I'm not making this yet another law debate, just answering your OP question and then will back off. Remember, Paul said the
mystery of law-less-ness (i.e.
secret/covert lawlessness) was ALREADY at work spreading in his day. To confirm this, just recall the multitude of people who would accuse Paul of preaching against the law, while he would
constantly argue or comment that he wasn't.
Fast-forward to today...compare our society from before the 10 commandments were publically removed to now after they've been removed. We don't even have genders anymore. The church has become an entertainment show. No one wants anyone to judge anything as "wrong" for fear of being accused of hate speech or intolerance. There are no more moral rules; no sense of right and wrong. Everything is fluid; chaos; based on how a person feels. Literal societal lawlessness abounds (which we frown upon) and yet the blueprint of our moral laws that governed that society (the commandments) is done away??
This belief was started in Paul's day by wolves in sheep's clothing but was made an official doctrine by the Papacy and the Catholic church and has spread through Protestant Christianity ever since like cancer.