The word revelation is used loosely in our time in relation to Christian theology. Some speak of God speaking to them, giving them a revelation through dreams, visions and prophecy. Someone may approach you and say God has revealed something to him about you. How are we to respond to such extra-biblical revelation?
The answer is to understand what revelation is, how God has spoken through the ages and how he speaks today. Such an understanding will free us from the error and danger of men and women who come with what they term revelation. One place in Scripture we can turn to in further answering the question about revelation is Hebrews 1:1-2.
Long ago, at many times and a in many ways, God spoke to our fathers by the prophets, but in these last days he has spoken to us by his Son, whom he appointed the heir of all things, through whom also he created the world.
When we say Revelation, we are speaking of how God has made himself known in human history. R.C. Sproul aptly says “Everything we know about Christianity has been revealed to us by God. To reveal means “to unveil.” It involves removing a cover from something that is concealed.”  Theologians identify two avenues by which God has revealed himself in human history, namely, General Revelation and Special Revelation.
General revelation, is, as named, general and is available to all. This revelation of God manifests in the world around us. God has revealed himself to all human beings through nature and no one has an excuse to deny the existence of God. Any denial is actually a suppression of the truth (Psalm 19:1-6; Romans 1:19-21).
Special revelation on the other hand is how God has revealed himself to humankind apart from nature and through special means unavailable to all. Special revelation is therefore salvific; that is, it leads to salvation. The Westminster Confession of Faith (WCF) highlights the inability of people to come to faith through General revelation: “Although the light of nature, and the works of creation and providence do so far manifest the goodness, wisdom, and power of God, as to leave men inexcusable; yet are they not sufficient to give that knowledge of God, and of His will, which is necessary unto salvation” (WCF 1.1). Special revelation varies in nature and this is precisely the point of the text when it says “at many times and in many ways.” Some of these many ways include theophanies, dreams, visions, and through prophets.
Clearly, we note that God is not a silent God but a God who has through human history revealed and made himself known specially: “God spoke to our fathers by the prophets, but in these last days he has spoken to us by his Son.” This sets a contrast between the prophets of long ago and Christ in these last days as God’s means of revelation. Prophets held a high place in Jewish religion for it is through them God spoke to the Old Testament people. “Our fathers” also in the text is to be understood as the Patriarchs of the Old Testament, who are the progenitors of the recipients. So God at a certain point in history; the past, revealed himself to the Jews by Prophets all recorded in the Old Testament.
In the the Old Testament which is also the Hebrew Bible or Tanak, the Jews have three main divisions — Torah (Law), Neb’im (Prophets) and Ketubim (The writings). You will recall when Jesus spoke with the two disciples on the road to Emmaus, he preached to them about himself from Moses (the Pentateuch or Torah) and all the Prophets (Luke 24:27). Prophets indeed held a high place in Jewish religion. When Paul said in 2Timothy 3:16 that “All Scripture is breathed out by God…”, he was speaking primarily of Old Testament Scripture made up of the writings of prophets–Major and Minor. It is in the same sense Peter’s words were written in 2 Peter 1:20-21.
Now moving from a lesser argument, that is, God speaking through the Prophets at different times and many ways, the author turns to a greater argument–Christ as the final agent of God’s revelation. Sinclair Ferguson in his book From The Mouth Of God identifies how God’s revelation of himself moved progressively to its culmination in the person of Christ.
First, it is historical: God has been active in history in order to show his power and love. Second, it is verbal: God has provided his own interpretation of his actions. He has given us a permanent record of his words … through…the pages of Scriptures. Third, it is progressive and cumulative. God gave his revelation in different ways and at different times. But now he has given his final revelation in these last days. Fourth, it is Christ-centred: God’s revelation reached its fulfillment when he spoke his final word to us in his Son, Jesus Christ. 
As we have seen, God’s revelation in the past (long ago) has been through agency of prophets through various means. But in these last days (the very day Jesus touched down to the earth until now) God’s revelation of himself culminated in the person of Christ: the God-man, the Immanuel. Christ is superior over all other forms of revelation. God has spoken his final words to us through Christ.
Since God’s final revelation has come, the implication therefore is that revelation has ceased for there is nothing new to reveal about God that has not been revealed in the person of Christ. And all of God’s special revelation has been recorded in Scripture to teach, reproof, correct, and train us in all ways necessary to please and glorify him. We therefore don’t need a prophet to speak into our life for direction or even a dream or vision to guide us. God’s written word is sufficient for in it we hear God’s word revealed through the Son: “This is my beloved Son: hear him” (Luke 9:35 KJV). Hearing the Son is only possible through the written word.
…therefore it pleased the Lord, at sundry times, and in divers manners, to reveal Himself, and to declare that His will unto His Church; and afterwards, for the better preserving and propagating of the truth, and for the more sure establishment and comfort of the Church against the corruption of the flesh, and the malice of Satan and of the world, to commit the same wholly unto writing; which maketh the Holy Scripture to be most necessary; those former ways of God’s revealing His will unto His people being now ceased (WCF 1.1)
I will finally conclude with the words of D. Martyn Lloyd-Jones as quoted in John MacArthur’s book, Strange Fire:
Again, we must note that often in the history of the Church trouble has arisen because people thought that they were prophets in the New Testament sense, and that they had received special revelations of truth. The answer to that is that in view of the New Testament Scriptures there is no need of further truth. That is an absolute proposition. We have all truth in the New Testament, and we have no need of any further revelations. All has been given, everything that is necessary for us is available. Therefore if a man claims to have received a revelation of some fresh truth we should suspect him immediately. 
1. Sproul, R. C.. Essential Truths of the Christian Faith ( United States Of America: Tyndale House Publishers, 1992), Kindle Edition
2: Sinclair B. Ferguson, From The Mouth Of God: Trusting, Reading, And Applying The Bible (Edinburgh: The Banner Of Truth, 2015), 7
3. John MacArthur, Strange Fire: The Danger of Offending The Holy Spirit With Counterfeit Worship (Nashville: Tennessee, Nelson Books, 2013), Kindle Edition.