You cannot separate what a person believes from who they are. This is the reason why doctrine is so important.
Some people say, “I do not believe in doctrine; I believe in the Lord Jesus Christ; I’m saved, I’m a Christian, and nothing else matters”. To speak in that way is to invite disaster.
We are to guard ourselves against being tossed “to and fro by the waves and carried about by every wind of doctrine, by human cunning, by craftiness in deceitful schemes.” (Eph 4:14).
If your doctrine goes astray your life will soon suffer as well. This is why the New Testament warns us against this very danger:
“Test everything; hold fast to what is good.” (1 Thess 5:21)
“Do not believe every spirit, but test the spirits to see whether they are from God, for many false prophets have gone out into the world.” (1 Jhn 4:1)
It’s in our best interest to study doctrine so that we may safeguard ourselves against erroneous and heretical teachings that are as common today as they were in the days of the early Church.
– Martyn Lloyd-Jones