In light of the foregoing habits of some, I'd like to provide a timely quote from one of the greatest expositors of the 20th century.
--Martyn Lloyd-Jones, Exposition of Ephesians
You cannot separate what a man believes from what he is. For this reason doctrine is vitally important. Certain people say ignorantly, "I do not believe in doctrine; I believe in the Lord Jesus Christ; I am saved, I am a Christian, and nothing else matters". To speak in that way is to court disaster, and for this reason, the New Testament itself warns us against this very danger.
We are to guard ourselves against being "tossed to and fro and carried about with every wind of doctrine", for if your doctrine goes astray your life will soon suffer as well.
So it behoves us to study the doctrines in order that we may safeguard ourselves against certain erroneous and heretical teachings that are as rife and as common in the world today as they were in the days of the early Church.