God, after He spoke long ago to the fathers in the prophets in many portions and in many ways, in theses last days has spoken to us in His Son...(Hebrews 1:1-2)
After introducing us to the proposition that God has spoken, the writer of Hebrews refines this claim in two ways. First, highlighting the historical authenticity and continuity of God's communication to humankind through the Scriptures, the author reminds the audience that "God [...] spoke long ago to the fathers in the prophets in many portions and in many ways" (Hebrews 1:1, NASB). Second, and foundational to the argumentation of Hebrews, the author declares that God "has in these last days spoken to us in His Son" (1:2). Accordingly, Jesus, the Son of God, is the ultimate means by which God has communicated His final, authoritative, divine, and living words to us and to all of humanity. Such claims are not only central tenets of Christian doctrine, but, for the recipients of the Letter to the Hebrews (and to us), the reality of these assertions serves as the substance for their (and our) hope, comfort, faith, and life. For this reason, the first major section of Hebrews ends with an exhortation that we "pay much closer attention to what we have heard [in/through Christ], lest we drift away from it" (2:1, ESV). The finality and reality of God speaking to us through Christ is of such weight that we cannot afford to act towards it with a Laodicean mindset.
The guarantee that God has spoken to us in His Son reveals in part both the nature of God as well as the nature of Christ. Again, as mentioned previously, we see God as an intimate and personal initiator whose words can be trusted because His communication is directly from Himself, for example through prophets and through Christ. Moreover, with regard to Jesus, God's Son, we see the perfection of God's spoken expression. For the writer of Hebrews, since "[Jesus] is the radiance of the glory of God and the exact imprint of His nature," God's word through Christ entails the divinity of Christ, the authority of Christ, and fulfillment in Christ (1:3; see also Colossians 1:15a, 19; 2:9; John 1:1-3, 18).