What God spoke to us in His Son has a much higher authority than the Old Testament.
Hebrews 1:1-2 God, after He spoke long ago to the fathers in the prophets in many portions and in many ways, in these last days has spoken to us in His Son.
God … spoke
God spoke – In Heb 1:1 God spoke in the prophets and in Heb 1:2 God spoke in the Son, but in both verses, it is God that spoke; not the prophets and not His Son.
If God had not spoken, we would have been without hope. – God exists outside the limitations of our physical space, time, and matter. He cannot be seen by our eyes or measured in a laboratory. He said,
“My thoughts are not your thoughts, neither are your ways My ways, … For as the heavens are higher than the earth, so are My ways higher than your ways, and My thoughts than your thoughts” (Isaiah 55:8-9).
We are not equipped to know anything about God. If God had not spoken, we would have been without knowledge of Him or without hope. But God has spoken and, therefore, we do have hope.
Long ago to the fathers in the prophets (Heb 1:1)
The letter to the Hebrews was written for Jews. – The letter to the Hebrews is very Jewish in nature. It has a strong focus on:
Moses (Heb 3:1-6);
The Exodus generation (Heb 3:7-4:11);
The Jewish sacrificial system (Heb 4:14-10:31);
The Old Testament heroes of faith (chapter 11) and;
The “heavenly Jerusalem” in contrast to Mount Sinai (Heb 12:18-24).
On the basis of this strong Jewish emphasis it is usually concluded that the letter was addressed to Jews who converted to Christianity, or even that it was addressed to a Jewish synagogue of which some members have accepted Jesus as Messiah, but others not.
The writer of Hebrews admits the Old Testament as the Word of God. – Both the writer and the intended audience were trained in the Jewish Scriptures. The writer in Heb 1:1 affirms the Old Testament as the Word of God. His ultimate purpose was to show the superior claims of the gospel and to lead them away from confidence in the Old Testament rites, but he will use the Old Testament to substantiate his arguments. Therefore he first affirms their belief in the inspiration of the prophets.
The fathers also belong to Gentile Christians. – The fathers include Abraham, Isaac, and Jacob. Gentile believers may correctly assume that “the fathers” belong to them as well, for Abraham is the spiritual father “of us all,” that is, of all true believers:
“so that the promise will be guaranteed to all the descendants, not only to those who are of the Law (the Jews), but also to those who are of the faith of Abraham, who is the father of us all” (Rom 4:16)
“if you belong to Christ, then you are Abraham’s descendants, heirs according to promise” (Gal 3:29).
God spoke … in many portions (KJV – parts) (Heb 1:1)
God did not speak through the prophets all at once. In the 39 books of the Old Testament, God revealed Himself in many portions.
God spoke … in many ways (Heb 1:1)
By whom did He speak? – Sometimes the Spirit spoke directly to His servants; sometimes through angels, or sometimes God even appeared Himself as the Angel of Jehovah, as to Abraham in Genesis 18.
How did He speak? – His methods of communication include direct 
communication, dreams, visions and impressions. Elijah, for example, once stood upon the mountain before Yahweh,
and there was a great and strong wind which rent the mountains, and broke the rocks into pieces; but Yahweh was not in the wind.
Then there was an earthquake, but Yahweh was not in the earthquake.
Then there was a fire, but Yahweh was not in the fire.
Then Yahweh spoke to Elijah in a “still small voice” (1 Kings 19:11-12).
In what form did He speak? – The forms in which His word is delivered include prophecy, poetry, proverbs, historical events and religious ordinances.
In these last days (Heb 1:2)
The early church expected Jesus to return soon. – The phrase “last days” is commonly interpreted as meaning ‘recently’. However, Jesus said, His disciples believed and the entire New Testament teaches that the Lord is coming soon. The author of Hebrews similarly wrote:
“Now once at the consummation of the ages He has been manifested to put away sin by the sacrifice of Himself” (Heb 9:26)
“all the more as you see the Day approaching. … For in just a very little while, He who is coming will come and will not delay” (Heb 10:25, 36-37).
The phrase “last days” elsewhere in the New Testament also implies the last days before Christ’s return:
“Know this first of all, that in the last days mockers will come with their mocking” (2 Peter 3:3)
“’and it shall be in the last days,’ God says, ‘that I will pour forth of My spirit on all mankind’” (Acts 2:17)
“But realize this, that in the last days difficult times will come. For men will be lovers of self” (2 Timothy 3:1-2)
It is therefore proposed that the phrase “these last days” indicates the writer’s belief that his generation was to be the last generation before Christ’s return. Please see Why did He Not Return in the First Century as He promised?
God … has spoken unto us (Heb 1:2)
This does not mean that the writer and/or his readers had actually heard Jesus, for they did not (Heb 2:3).
We should be astonished that the infinite and eternal God should speak to man; a speck of dust floating in the unending expanse of the universe. But it reflects God’s love for mankind; “For God so loved the world, that He gave His only begotten Son” (John 3:16).
In his Son (1:2)
To become a human being, His Son emptied Himself of glory, power and wisdom. Jesus said, “before Abraham was born, I am” (John 7:58). The Son shared the Divine glory before the world was, but He “emptied Himself” (Phil 2:7) when He came into the world. That means that He laid aside His glory and power, and even His wisdom, “taking the form of a bond-servant” (Phil 2:7). He became a helpless human baby, had to develop like any other human being, and was dependent on God for everything. He said, “the Son can do nothing of Himself, unless it is something He sees the Father doing” (John 5:19), and “I cast out demons by the Spirit of God” (Matt 12:18). But even though Christ emptied Himself, He remained Who He previously was before. These things we have to accept by faith, for we are unable to understand it.
The title “Son” signifies His unique relationship to God, just like the title “Son of man” designates His relationship to man. The Jews understood the title “Son of God” to mean equality with God:
Jesus said, “My Father is working until now” (John 5:17). “For this reason the Jews were seeking all the more to kill Him, because He not only was breaking the Sabbath, but also was calling God His own Father, making Himself equal with God.” (John 5:18).
John 10 records Jesus saying “I am the Son of God” (John 10:36). For that reason, the Jews wanted to stone Him, saying, “because You, being a man, make Yourself out to be God” (v33).
The most wonderful event in history – The most wonderful event ever in the existence of mankind is that the Son of God should have come from heaven to teach mankind. Yet, equally amazing, how few listened to Him when He was on the earth, and how few still regard Him today. People have no interest in Him, and refuse to listen to what He has to say about the unseen and eternal world.
The New Testament is God’s message in His Son. The Four Gospels—the first four books of the New Testament—record God speaking to us in His Son, but Acts and the New Testament letters interpreted and elaborated what Jesus taught. Therefore the entire New Testament may be considered to be what God “has spoken to us in His Son”.
The gospels are the foundation of the New Testament. Some Bible interpretations view the gospels effectively as part of the Old Testament and teach that the New Testament letters represent true Christianity. But according to Hebrews, the foundation of Christianity is what God spoke to us in His Son.
The New Testament has a much higher authority than the Old Testament. The Old Testament contains solemn messages to mankind which God gave to the prophets, endowing them with more than human wisdom and eloquence. But how much more important is the message which is brought by his own Son? Throughout the letter, the writer contrasts the old and the new and elevates the new above the old. In the current verses, the old is how God revealed Himself through the Old Testament prophets, and the new is how He revealed Himself through His Son. With this contrast, the writer is saying that, what God has spoken to us in His Son, has a much higher authority than the Old Testament, and therefore imposes on us the highest obligation to attend to what He has said. This is the main message of Hebrews 1:1-3.
The New Testament clarifies many issues that were unclear in the Old. There is a great variety of subjects which we now, with the benefit of Christ’s teachings, see clearly, which were very imperfectly understood by the teaching of only the Old Testament prophets. Among them are the following:
(a) The character of God:
“No one has seen God at any time; the only begotten God who is in the bosom of the Father, He has explained Him.” (John 1:18)
“Nor does anyone know the Father except the Son, and anyone to whom the Son wills to reveal Him” (Matt 11:27)
(b) How man may be reconciled to God: Even the sins committed under the first covenant are taken away through the sacrifice of His Son (Heb 9:15; 10:4; 11:40; Rom 3:25).
(c) God’s moral principles: Prophets had delivered many moral principles of great importance, but the purest and most extensive body of moral principles on earth are found in Christ’s teachings.
(d) The future state: Jesus revealed the doctrine of the resurrection of the body and the certainty of a state of future existence. What the Sadducees previously were able to dispute, is stated irrefutably in the New Testament. The Saviour raised up more than one to show that it was possible; and He was Himself raised, to put the whole matter beyond dispute. He also revealed the certainty of the future judgment of all mankind.
Conclusion
Hebrews does not have an introduction as we would find in other letters. The first word in Paul’s letters, for instance, is always his own name, followed by the name of the church or individual to whom he wrote.
In Hebrews, the first three verses serve as an introduction, but also immediately confront the reader with the main theme of the entire epistle, which is the superiority of Christ and His message. The first three verses argue that Christ is superior to the Old Testament prophets, for He is God’s Son—the exact representation of God’s nature—and through Him, God made everything and through Him God still upholds everything. But that is not the writer’s ultimate goal. His real message is that Jesus’ message, as recorded in the New Testament, is superior to the Old Testament prophets.