Sometimes alternate post are not competing with original posts only complimenting them. I seek to compliment and amplify Affable’s post which has already more simply stated. Partly to help me straighten it out in my own mind!
I am gathering my results to your question more from a word study using the Theological Dictionary of the New Testament, Gerhard Kittel, but not quoting him directly. Rather I used his observations to help me collect my own thoughts that I have encountered in many places.
The main problem with defining ‘prophecy’ is that you must work your way back to the ‘prophet’ and like many words in the Bible, there are various meanings, not just one. For example ‘fear’ in the Bible has so many meanings, sometimes almost contradicting each other, that you need a spreadsheet just to sort them. It is therefore the concepts that we must learn, and then we can determine the right meaning of the word as it is found in different contexts and apply our knowledge to extract its meaning in that location. Sometimes it seems bad theologians are simply those who fix one meaning to a word and then distort the Bible accordingly.
So what are the Biblical concepts of ‘prophet’?
First, the Bible early on indicating who a prophets was:
Now return the man’s wife, for he is a prophet, and he will pray for you and you will live. But if you do not return her, you may be sure that you and all who belong to you will die.” (NIV Genesis 20:7)
Abraham did not do a lot of future predictions but as he represented God from among all others and in this instance acted as a mediator in intercessory prayer, he was the basic meaning of a prophet. The things Abraham had to say in general may be considered prophetic, or prophecy, due to his peculiar role.
More clearly does this high authoritative role appear in Moses, where when Aaron is made to be his mouthpiece, Moses becomes the symbol of God to Pharaoh:
Then the Lord said to Moses, “See, I have made you like God to Pharaoh, and your brother Aaron will be your prophet. 2 You are to say everything I command you, and your brother Aaron is to tell Pharaoh to let the Israelites go out of his country. (NIV Exodus 7:1-2)
This is the foundation of the high level authoritative office of prophet and the function in it, representing God’s will, currently and sometimes in the future.
There is also another sense of prophet found later on in the scriptures where there were actual schools of many prophets. For example we meet groups of prophets after Samuel anointed Saul and said to him:
As you approach the town, you will meet a procession of prophets coming down from the high place with lyres, timbrels, pipes and harps being played before them, and they will be prophesying. The Spirit of the Lord will come powerfully upon you, and you will prophesy with them; and you will be changed into a different person. (NIV 1 Samuel 10:5-7)
These prophets are represented as having an ‘experience of God’ so that it is more ecstatic then it is necessarily predicting the future. In this sense even inspired worship, even through just instruments at times, in this experience of God is prophecy. The musicians were called to prophecy under this sense of the word:
David, together with the commanders of the army, set apart some of the sons of Asaph, Heman and Jeduthun for the ministry of prophesying, accompanied by harps, lyres and cymbals. Here is the list of the men who performed this service: (NIV 1 Chronicles 25:1)
All these men were under the supervision of their father for the music of the temple of the Lord, with cymbals, lyres and harps, for the ministry at the house of God. (NIV 1 Chronicles 25:6)
As the Old Testament progresses this ecstatic experience of prophecy diminishes and the actual writings of prophets and individual prophets come to the forefront. This may be considered the true developed office. In this sense we find that period of the prophets indicated in the New Testament more frequently:
“Indeed, beginning with Samuel, all the prophets who have spoken have foretold these days. And you are heirs of the prophets and of the covenant God made with your fathers. (NIV Acts 3:24-25)
This final authoritative official office of the Prophets focused on the word of the prophets as they were written and as they foretold of Christ.
The Lord was with Samuel as he grew up, and he let none of Samuel’s words fall to the ground.(NIV 1 Samuel 3:19)
This formal office of prophet ended with John, as the whole purpose of the position was to predict Christ:
For all the Prophets and the Law prophesied until John. (NIV Mathew 11:13)
As we leave John and transition to the New Testament, the twelve Apostles become the new high authority, even higher than the prophets:
And God has placed in the church first of all apostles, second prophets, third teachers, then miracles, then gifts of healing, of helping, of guidance, and of different kinds of tongues. (1 Corinthians 12:28)
However just as the term prophet has many senses even Apostle may refer to something other than the 'high authoritative office of the twelve', who were called by the visible Christ, but that is another subject.
There is another difference in the New Testament that carries the word ‘prophecy’ into a new sense. Unlike the Old Testament where the Prophets had high authority and who alone seemed to have the Spirit, in the last days this role would change. Upon the ending of that high role, some aspects of it, namely the experience of the Spirit and even gifts of seeing God’s will for our current situation and even in Acts and other places a gift of prophecy that could predict future events was long foretold by Joel:
“And afterward, I will pour out my Spirit on all people.
Your sons and daughters will prophesy,your old men will dream dreams,
your young men will see visions. Even on my servants, both men and women,
I will pour out my Spirit in those days. (NIV Joel 2:28-29)
In this sense under a new meaning of prophecy, after the high official office ended, everyone prophecies by experiencing the Spirit and some may also (at least in those days) have a gift to predict future things by that same Spirit.
With respect to Jesus he is not directly a Prophet, Apostle, Priest, or King but is Messiah making him The Prophet, The Apostle, The Priest, The King and so none who claim to be those things in such a way as to imply there is something more needed are false, apostles, prophets, etc.:
Therefore, holy brothers and sisters, who share in the heavenly calling, fix your thoughts on Jesus, whom we acknowledge as our apostle and high priest. (NIV Hebrews 3:1)
Just as the Prophets ended in that their primary purpose was to write down those prophecies which were fulfilled as Christ appeared, so as the twelve Apostles established the doctrines of the church in the New Testament, having completed their task the office, in that sense also ceased. We now have teachers and preachers who make known God’s word to us, and in this sense they maintain this ancient tradition of prophecy. All prophecy speaks of Christ, for this is the current and future will of God, that we adore him, in the Spirit of worship and love.
Note: Whether the gift of prophecy in narrow future foretelling sense may, or may not exists today is back into the cessation, non-cessation argument, or somewhere in-between, which is not directly related to the overall meaning of 'prophets' who 'prophecy'.