Please read about what the Nicene Council accomplished.
The Council of Nicaea was the first council in the history of the
Christian church that was intended to address the entire body of believers. It was convened by the emperor
Constantine to resolve the controversy of
Arianism, a doctrine that held that
Christ was not divine but was a created being. The council deemed Arianism a
heresy and enshrined the divinity of Christ by invoking the term
homoousios (Greek: “of one substance”) in a statement of faith known as the Creed of Nicaea.
Let's not make more of it than what it was, or give too much credit to Constantine for many changes that were implemented by his sons or others later on.
As to the Dead Sea scrolls they did nothing more than give additional insight into the daily lives of the Essenes or those eccentric Jewish religious sects
like them that rejected the Pharisees and lived on the edge of the city in commune like establishments and who collected libraries. The scrolls that dealt with their communal rules shed light only on them. Light is shed on their theology but nothing in the Dead Sea Scrolls changed our understanding of the times before Christ.
A good New Testament Survey book would be the best way to learn about the times from the Babylonian Captivity up to the appearance of Christ and what the culture, politicly, religiously, etc was like. There is a huge amount of documented information to give us this understanding and all of the New Testament Survey books are similar in the way they present it. The Dead Sea Scrolls did not add much if anything to that.
We don't even know for sure how many of the pseudonymous works (writings under a false name) they took serious or just collected as literature to refute. They did not add anything to our knowledge of the times before Christ. Writings such as the Maccabees, and the historians Tacitus, Heroditus, Thicydides and many others had already provided much information about times between the Testaments and the Dead Sea Scrolls added nothing to this.
I think it would help to read a Wikipedia article on the Dead Sea Scroll for starters and this will help you discern fact from fiction when people claim too much about the Dead Sea Scrolls.
The most significant contribution of the Dead Sea Scrolls was that of providing a copy of Isaiah that was 900 years older than any copy we had in extant before this discovery. By comparing it to existing manuscripts there were not significant differences and this disproved the argument often suggested by secular college professors that we cannot know if our current copy of scriptures is what the original authors wrote because they have been copied so many times they are probably full of mistakes. The copy of Isaiah nearly 1000 years older having do difference put that argument to rest.
The unbelievers still say it but they just make themselves out to be uneducated when they say it now.
Oh. To answer your question;
If we do not do our own bible study to determine whether our church doctrine is the best interpretation of scriptures on those doctrines and blindly follow them we could be guilty of idolatry, placing that denomination higher in our hearts that the Lord Jesus Christ.
If in our study we discover that our church doctrine is making a mistake in interpreting scripture, for example making statements that the gifts of the Holy Spirit ceased when the book of Revelation was completed, but we do not find this in the scripture and we do not feel comfortable accepting this interpretation, (i.e. we feel the check of the Spirit) but we then choose to accept it anyway because "they know more than me" or "I don't want to rock the boat" then we are committing idolatry and placing the denomination or church teaching higher than our love for truth.
We are responsible to walk in the Light that God has given us. Even if it means withdrawing from that fellowship and finding one who's doctrines are more in line with the interpretation of scriptures as you have discovered for yourself.
Sometimes it does not really matter that much. You might not agree with an interpretation of something that your church is teaching but it is not a deal breaker. For example the timing of the rapture.