Doctrine is that which is taught as true.
In Romans 2, Paul speaks to a Jew and describes them as having a form of doctrine.
“Behold, thou art called a Jew…which hast the form of knowledge and of the truth in the law.” – Rom 2:17, 20
In Romans 6, Paul speaks to the sinner now saved by grace through faith as also having a form of doctrine.
“God be thanked, that ye were the servants of sin, but ye have obeyed from the heart that form of doctrine which was delivered you.” – Romans 6:17
Not all doctrine in the Bible is the same. The form of doctrine Paul refers to is different than the form of doctrine given to the Jew in time past.
It is not enough to be doctrinal; you must know that form of doctrine which was delivered you by God.
All scripture is doctrine for someone. The question is, “Which form of doctrine was delivered to us?” It will also help to ask, “Through whom in Scripture did God deliver this doctrine to us?”
God gave Moses the law to give to the Jew as their doctrine.
God gave Paul the dispensation of the grace of God to give to all men as their doctrine. If you are under grace, you are not under the law (Rom 5:21; Rom 6:14).
This is how you start to rightly divide.
For your edification,
Justin “re-formed doctrine” Johnson