During the Protestant Reformation, people were looking for a word from God, just as they search for a word from Him today. The Reformers, including individuals such as Martin Luther and John Calvin, proclaimed that there is but one place to find special revelation—the Scriptures of the Old and New Testaments. They asserted the doctrine of sola Scriptura: the only source of special revelation for the church today is the Bible; thus, the Bible is the only infallible authority for the church.
Since God has provided special revelation to people in other forms such as dreams (Gen. 40), how do we know special revelation today is found nowhere else besides Scripture? Today's passage helps answer that question. God did speak to His people in various ways and at various times. Yet "in these last days"—this era wherein the Lord is fulfilling His promises—He has spoken finally and definitively in His Son (Heb. 1:1–2). So, we look for special revelation nowhere but in Christ.
However, this does not mean we look only to the actual words that Christ spoke during His earthly ministry. Those words are included, of course, which means we receive the Gospels and other portions of the New Testament that record what our Lord said while He walked the earth (for example, 1 Cor. 11:23–25) as special revelation. But we also receive as special revelation that which Christ affirmed as special revelation, which is "the Law of Moses and the Prophets and the Psalms" (Luke 24:44). This threefold designation of special revelation, we will see in due time, is coterminous with the thirty-nine-book Old Testament canon that we follow as Protestants.
What of the New Testament books that do not record what our Lord said during His earthly ministry? We receive those as special revelation as well because of the uniqueness of the Apostolic office. In the ancient world, as Dr. R.C. Sproul often observes, the title apostle was used even in the secular realm for those who had the full authority to speak on behalf of a higher official. Jesus' Apostles were His official spokesmen who bore His full authority, so their writings are as much the words of Jesus as any other portion of Scripture.
Only the Apostles speak with an authority equivalent to Jesus' during the new covenant era. There are no Apostles today because there are no living eyewitnesses of the resurrection to confirm other Apostles (Acts 1:12–26; Gal. 1:18–2:10). Thus, special revelation ended with the death of the last Apostle in the first century.
Many people today claim to be Apostles. However, to be an Apostle, one must be an eyewitness of Jesus' resurrection or be confirmed as an Apostle by other resurrection eyewitnesses (Acts 1:12–26; Gal. 1:18–2:10). This is impossible in our era, so there are no living Apostles giving us special revelation. We must be content with what we have—the Apostolic and prophetic words of Scripture. To look beyond these for a word from God is to look in vain.