purpose:

God still wants the revelation of His will to be vocalized. So He has established the prophetic ministry as a voice of revelation and illumination which will reveal the mind of Christ to the human race. He also uses this ministry to give specific instructions to individuals concerning His personal will for their lives. ...

The ministry of the prophet is not, of course, to bring about additions or subtractions to the Bible. Any new additions accepted as infallibly inspired would be counterfeits, false documents containing delusions that lead to damnation. Instead, the prophet brings illumination and further specifics about what has already been written. And the Holy Spirit’s gift of prophecy through the saints is to bring edification, exhortation, and comfort to the Church (1Cor.14:3). ...

confirmation:

The Holy Spirit whispering the thoughts of Christ within a Christian’s heart is obviously God’s ideal and divine order for communication. But what an individual has sensed in his or her spirit should be confirmed: God’s counsel is that every word needs to be witnessed to and confirmed in the mouth of two or three witnesses (2Cor.13:1). This is a critical role that can be fulfilled by the prophetic voice.

not a substitute:

Of course, personal prophecy must never become a substitute for the individual’s responsibility and privilege of hearing the voice of god for him or herself. God is a jealous God and is not pleased when we allow anything to hinder an intimate relationship and personal communication with Heaven, even if the hindrance is from a ministry He Himself has ordained. Personal prophecy must not take the place of our duty to fast, pray, and seek God until we hear from heaven ourselves!

discovering God’s word, will, and way:

Though personal prophecy can play an important role in helping Christians make decisions, it is by no means the only way the Holy Spirit uses to reveal God’s will and way…. The most accurate method of making sure you do everything in harmony with Heaven is to follow these “three W’s” of decision making. Determine God’s Word on a matter, His specific will about it, and His way to fulfill it. These are like three traffic lights that must all be “green” before we can proceed on our way.

*excerpted from dr. bill hamon's "prophets, pitfalls and principles" (destiny image, 1991)