Religion changes with it.
For example, sexism is strongly promoted in the Bible, but most Christians aren't sexists.
I have more respect for those that adapt their religious beliefs to modern standards instead of stubbornly clinging to their outdated stances.
If people who don't follow their religion to a T can't be considered "true believers", that leaves a very small number of "true believers".
The average believe does have the right to pick and choose what parts of his/her religion to follow and can still call himself/herself a "true believer." For one thing, who gets to decide that one person is a true believer and another is not? Also, whose interpretation of religious texts are correct? Many people believe that religious texts have been altered by men to control the masses. If a person feels that s/he is a true believer, it is their right to call themselves that if they choose to.
I am an atheist but I don't see any problem with an "average believer" picking and choosing what to believe in and what not to believe in. Historically speaking Jesus was a Rabbi that preached good will and equality in a time when the Romans were crucifying everyone who spoke against them. He may have wrote some of his speeches down but historians are unsure. The first guy to turn Jesus into a god and start writing about Christianity was Paul (Saul) and he wrote 14 of the testaments. Catholic actually means "universal" or "of the whole". In my opinion all religions are up for interpretation otherwise we would not have Protestants, Lutherans, or Christians. In Islam its Shiites, Sooni, and the Ishad.
Our beliefs matter to only us and not of other people, If we see ourselves to be true believers even if we chose only to believe in a few conditions of the chosen religion. Why bother trying to force someone to do a full submission to another person's beliefs/ideals when it does not really affect anyone at all?
I once heard that reading the bible without doctrine is like driving through Russia without a roadmap. Your gonna get lost, and most likely profoundly lost. Christianity is one of the few religions where doctrine is very important... In fact probably THE most important thing about Christianity. It matters what you believe! That is actually an odd thing as far as religion goes, but to many Christians they could not imagine a religion that does't care what you believe.
Pagans had no doctrine... It didn't matter what pagans believed about their gods, or even if they actually believed in their gods, it only mattered that they worshiped them and gave sacrifices and participated in public events honoring the gods. There was no such thing as heresy in paganism.
Jews have a bit more doctrine, they believe in the one true God and thats important. But if you believe in that one true God a really really really big bunch it does't make you a better Jew. What makes you a better Jew is to follow the Jewish law, honor Jewish holy days, eat the right foods etc. What you do makes you a better Jew... Theoretically they all believe the same thing.
For Christians it matters what you believe... And heresy was a big problem in early Christianity, and even though Christians are more tolerant now there are still a wide range of christians that believe a wide range of things... Because thats what they value. How many times have you heard a Christian say something like "well I believe in Jesus and am a spiritual person but I don't believe in the institutions of the church or organized religion. I prefer a personal relationship with God." That statement is really only possible in Christianity, were you can feel you are 100% correct and 100% saved by Jesus by just sitting on your butt at home and believing in him a really really really lot. The problem with this is that there are a lot of christians out there that have no guidance, no direction and no knowledge about the Bible and its importance and its place in Theology. Many are in fact guilty of fundamental heresies. People use and misuse the Bible to attack and defend a wide range of positions because they are not operating within Christian Theology. Too many Christians are "lost in Russia"!!
To be a believer suggests that one subscribes to the core tenets of a religion. So called "believers" can't selectively chose what they wish to believe and not. One should never claim to be something they know nothing about.
This can be confusing for some religions. In particular, monotheistic religions like Christianity, Islam, and Judaism. These religions are made up of several books with various authors. This can be confusing for readers who may convolute the books if they fail to comprehend the differences. For example for someone to subscribe to Christianity they must follow the teachings of Jesus of Nazareth, not the Old Testament. Not to pick on Christians but many tend to fail to understand the differences among the collection of books in the Bible.
I dont think anyone who is not in a place of religious authority (and really even those who do have it) has no authority to pick and choose what parts of their religion they follow and still consider themselves a part of the faith. For example people who claim to be true christians but ignore all the horrible stuff in the bible. Who decides what parts of the bible are more important to God than others? I personally think that the whole belief system falls apart when you take it into your own hands like that.
I mean if you feel happy to think that the parts in the bible (for example) about hating gay people or not wearing clothes of mixed materials is not true, or added by mortals or simply not important then how do you draw the line at what is? If it was made up by people surely all of it could have been made up by people? On an issue that is as supposedly immutable as the word of God I think you need to do all or nothing to consider yourself a true follower.
You can't choose what parts of law to follow and then say you didn't break the law. You can still be a believer but not a true one. For example there is a part in the Christian bible that says that any woman who shows her legs, should be stoned to death. Does anyone do this today? In most places no. There is nothing wrong with being a believer but saying you are true when you only follow parts of a religion is wrong.
Yes I accept times and morals and social attitudes have changed massively since the time scriptures were wrote, however religions are a way of life, and (using Christianity as an example) if we strive to live like Jesus and are made in God's image, then we should live like Jesus did. No matter how things change, the religious message is always the same, and no one on this earth would be able to alter the bible or any other religious passages as no one on this earth knows how Jesus would act in our day and age; just estimate from his previous actions. That is not a reliable basis to go by. If you were a true believer then you would completely accept and agree with EVERYTHING as you are TRUE to your religion. If you don't agree with everything it doesn't make you a bad person, everyone's entitled to their own opinions, it just means you're not fully in acceptance of it.
HOWEVER in the context of a true believer being one who regularly attends church/mosque, prays, takes pilgrimages etc, then yes they can definitely still be a true believer. You can have someone who 100% shares the same views as in the bible, but never go to church, whereas someone who may support gay marriage but still goes to church every Sunday would still be a devout catholic