A just God can only punish, or reward, real choices. If we have the real choice to accept or reject we can be rewarded or punished for it.
Look at all the different belief groups in the world, inside and out of Christianity. Do they have faith? Almost everyone does. Do they love truth. If you ask them, they will say, "Most definitely". Are their core beliefs true. Most will say that their core beliefs are unquestionable truths... kind of like what we get on all sides of the Calvinism issue as well. And what's more, all the groups that believe in a gospel believe the gospel is simple. They just believe "different" simple gospels.
How does this happen? It's God's design. The people Paul was writing to are compared to the lost who reject a love of the truth so as to be saved in verses 10-12. But they pass the test.
2Th 2:10 and with all the deception of wickedness for those who perish, because they did not receive the love of the truth so as to be saved. 11 For this reason God will send upon them a deluding influence so that they will believe what is false, 12 in order that they all may be judged who did not believe the truth, but took pleasure in wickedness. 13 But we should always give thanks to God for you, brethren beloved by the Lord, because God has chosen you from the beginning for salvation through sanctification by the Spirit and faith in the truth.
This means that this is a truth for all time. "For this reason", i.e. because of the choice that they make...
But do they know what choice they are making? Do they have the ability to make a choice? Does God reward and punish choices? Let's look at Rom. 1:18-32
Rom 1:18 For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men who suppress(You cannot suppress what you do not know exists. This is an act of will) the truth in unrighteousness, (The following describes how God seeks all men, even the lost who will never receive Him.) 19 because that which is known about God is evident within them; for God made it evident to them. 20 For since the creation of the world His invisible attributes, His eternal power and divine nature, have been clearly seen, being understood through what has been made, so that they are without excuse. (God makes it so that no man has any excuse for not seeking Him and then leaves the choices to Him.)21 For even though they knew God, they did not honor Him as God or give thanks, but they became futile in their speculations, and their foolish heart was darkened. 22 Professing to be wise, they became fools, 23 and exchanged(A choice, an act of will. A decision) the glory of the incorruptible God for an image in the form of corruptible man and of birds and four-footed animals and crawling creatures. 24 (Consequences for bad choices)Therefore God gave them over in the lusts of their hearts to impurity, so that their bodies would be dishonored among them. 25 For they exchanged(Another choice. Another act of will.) the truth of God for a lie, and worshiped and served the creature rather than the Creator, who is blessed forever. Amen. 26 For this reason (God responds to mans choice and gives him consequences for them.) God gave them over to degrading passions; for their women exchanged the natural function for that which is unnatural, 27 and in the same way also the men abandoned the natural function of the woman and burned in their desire toward one another, men with men committing indecent acts and receiving in their own persons the due penalty of their error. 28 And just as they did not see fit to acknowledge God any longer(Another act of will. Another choice.), (And God's response.) God gave them over to a depraved mind, to do those things which are not proper, 29 being filled with all unrighteousness, wickedness, greed, evil; full of envy, murder, strife, deceit, malice; they are gossips, 30 slanderers, haters of God, insolent, arrogant, boastful, inventors of evil, disobedient to parents, 31 without understanding, untrustworthy, unloving, unmerciful; 32 and although they know the ordinance of God, that those who practice such things are worthy of death (Even while they are rejecting, suppressing and exchanging the truth of God for a lie, God makes sure that they retain the knowledge of their choices, and the full awareness of what those choices will result in.) , they not only do the same, but also give hearty approval to those who practice them.
If they cannot respond other than what they choose to respond with here, then God is unjust to judge them for it. i.e. spanking a 2 month old baby for dirtying a diaper is not just. Why? There is no real way for a baby to make any choice that will make a difference. The good news is, God is going to let everyone who falls short and is heading for hell to judge Him to see if they really did have these choices, if they really could have chosen to accept Him. If He really did give them absolutely everything needed to end up on the opposite side of an outcome of eternity in hell. If God is found to have lied, and they aren't real choices, God will fall short during this judgment.
Rom 3:3 What then? If some did not believe, their unbelief will not nullify the faithfulness of God, will it? 4 May it never be! Rather, let God be found true, though every man be found a liar, as it is written, "THAT YOU MAY BE JUSTIFIED IN YOUR WORDS, AND PREVAIL WHEN YOU ARE JUDGED." 5 But if our unrighteousness demonstrates the righteousness of God, what shall we say? The God who inflicts wrath is not unrighteous, is He? (I am speaking in human terms.) 6 May it never be! For otherwise, how will God judge the world?
God didn't fail. Men choose. It's a real choice. Men choose hell. God is not unrighteous. Everything He says and does is justified. People have no excuse for making the wrong choices. NONE! Ergo, when God allows them to judge Him, no fault can be laid at God's feet. They have every opportunity. They choose to suppress, reject, and exchange it for a lie.
The religious, non-Christians also have a zeal in accordance with their beliefs about God. They can find everything in scripture to justify not accepting Jesus as their Lord, God and Savior using scripture. Everyone who uses scripture can justify their beliefs, their lives, their actions ... using it.
Rom 10:1 Brethren, my heart's desire and my prayer to God for them is for their salvation. 2 For I testify about them that they have a zeal for God, but not in accordance with knowledge. 3 For not knowing about God's righteousness and seeking to establish their own, they did not subject themselves to the righteousness of God.
We can go to scripture and end up believing anything at all under the sun. Everyone can justify any belief or belief set out there. Read that 2Th. 2:10-13 passage again. Even the many, the "Many" on the broad path that leads to destruction have everything they need to know that their beliefs are truth. "Lord, Lord, did we not ___ in Your Name, and in Your Name ..." "Depart from Me .... for I never knew you." Mat. 7 is about how those who believe they are Christians, probably 99.95 of them, end up knowing their beliefs are facts and that all opposing beliefs are lies. They have unquestionable faith that Jesus is their Lord God and Savior, and since their core beliefs are fact, being open-minded to altering the absolute truth of their core beliefs for anything else, which is obviously a lie, will not happen. Mat. 7:6
Thus, why would they ever seriously consider that their core beliefs are wrong? Looking at anything "else" is considering exchanging truth for a lie. No one is open to that. And to suggest that one of them might be in the "Many" of the lost Christians on the broad path that leads to destruction is just asking for a fight. But no group that believes themselves to be Christians ever sees themselves as being in the group that falls short. Suggest they are and you will see anger and the end of a discussion.
Mat 7:6 "Do not give what is holy to dogs, and do not throw your pearls before swine, or they will trample them under their feet, and turn and tear you to pieces.
But if the universal reason for all of the lost is 2Th. 2:10-13, i.e. refusing to receive a love of the truth God builds right into every man so they have a real choice and "no excuse" to pair it up with, we should see some similarity in what all the people in the world with false beliefs do to hold fast to their positions as "fact". Interestingly...
People who want to hold fast to what they “want to believe” “as” truth:
1.) Gather whatever they can “use” to prove what they “want to believe” to be truth.
2.) Accumulate all evidence they believe proves all opposing views incorrect.
3.) Assume their beliefs are unquestionable truth, and interpret everything in such a way as to make it all support, or at least not negate, their beliefs. Think about it. If your beliefs are unquestionable truths, all “valid” data, must support … or at least not negate, your infallible beliefs, right?
4.) Reinterpret, ignore, discredit, invalidate … anything that doesn’t seem to fit with their views, Why? Our beliefs are “Fact” Valid data interpreted correctly can’t contradict the facts.
5.) Gather all the other experiences, feelings, data … to solidify their beliefs such as signs, wonders, spiritual gifts or facts about your belief group. Things like: we have a burning in the bosom, we speak in tongues, we perform signs or wonders, a statue of Mary came to life and told us our belief groups views are correct, we have prayed to God for the truth and received “feelings” or even signs from heaven. Or, on a more concrete level: Our belief group is the oldest, largest, fastest growing, wealthiest, has the most experts with doctorates… Include anything that adds assurance that your views and belief group have the most truth.
These are the things we do "if" we just want to believe what we want to believe, and have reasons for discarding the rest. This process closes our eyes, ears and hearts to even considering anything else. This process allows all the people from every group believing themselves to be Christian to believe the gospel is simple, while believing completely different “simple” gospels.
Everyone in every group gets what they want. Every belief group knows they love the truth and have the truth. Every group uses this exact same Methodology. But since this Methodology can be used to prove anything true, or the exact same things false, at will, it is perfect for those who just want to keep believing what they already believe.
If you use the Methodology above, you can be a Moslem, Mormon, Jehovah's Witness, Roman Catholic, Calvinist, Arminian, ... anything at all, every belief under the sun, and "know" your beliefs are fact till the day you die. Ask any group. They all have these things and they all know that when you interpret all valid data correctly, their core beliefs are "fact". The more they "do" the Methodology in 1-5 above the more cemented or hardened into their beliefs they become, and the more their eyes and ears are closed to ever seriously considering anything else, which, by definition is all lies and error.
No one ever gets "from" their beliefs "to" truth using that Methodology above. Just like the 2Th. passage says. God makes sure that if they do not love truth they all have what they need to hold fast to their beliefs. It's their choice. God gives them over to it.
Joh 6:28 Therefore they said to Him, "What shall we do, so that we may work the works of God?" 29 Jesus answered and said to them, "This is the work of God, that you believe in Him whom He has sent."
The one work man does that makes all the eternal difference.