I am finally carving out some time to read Wayne Grudem's The Gift of Prophecy. I've had it for about 5 years and knew one day I would want to read through it. Chapter 6 is extremely helpful for me as I think about the NT gift of prophecy.
It is important to note that the first 5 chapters do a great job of establishing the fact that NT prophecy is NOT the same as OT prophecy. OT prophecy was speaking the very words of God and thus authoritative. NT prophecy is speaking merely human words to report something God brings to mind.
Here are some nuggets:
The Nature of Prophecy:
2 factors that are essential to prophecy:
1. a revelation from the Holy Spirit.
2. a public report of that revelation.
The Nature of Teaching:
1. based on Scripture, not on a spontaneous revelation.
2. seeks to interpret and apply the Scripture.
This is why Paul allowed women to prophesy but not teach. Teaching carries much more authority than prophecy.
So here is the distinction: "If a message is the result of conscious reflection on the text of Scripture, containing interpretation of the text and application to life, then it is (in NT terms) a teaching. But if a message is the report of something God brings suddenly to mind, then it is a prophecy. And, of course, even prepared teachings can be interrupted by unplanned additional material which the Bible teacher suddenly feels God is bringing to his mind--in that case, it would be a 'teaching' with some prophecy mixed in" (p. 120).
"Prophets in the NT churches reported in their own words something which, it seemed to them, God had forcefully brought to mind. So teaching based on the written Word of God had far greater authority than occasional prophecies which the speaker thought were from God" (p. 122).
In prophecy, one can never be 100% sure it is from God. Thus, it does not carry near the same weight as a teaching from Scripture (which is certainly from God).
I would highly recommend that you read The Gift of Prophecy if you want to study this issue in more depth. It is a well written, engaging, and Bible-saturated teatment of the topic.