Due Diligence

Do not take my word for it. Study and show yourself approved before God. Be sure to consider the context of the Bible when reading it, and let the Bible interpret itself.

2 Timothy 3
16 All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness: 17 that the man of God may be perfect, thoroughly furnished unto all good works.

Extra-Biblical does not necessarily mean anti-Biblical or un-Biblical. It means something acquired outside of the Bible. This could be from another text, or from an experience some one has had while walking with God. All references should find their substantiation in the Word: if it is spoken of the Holy Spirit it can be confirmed in the Bible.
1 John 5
7For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one. 8 And there are three that bear witness in earth, the Spirit, and the water, and the blood: and these three agree in one.