We are living in the last days. During the last days God has spoken by the Son. The Letter to the Hebrews explains that what God has said to us in Christ is indeed His last Word. Every chapter emphasizes this central fact. God's message in Christ is His last Word because it is His deepest Word.
Nothing remains hidden.
He has said it all. Some people suspect that there might be dark and hidden facts about God, things you never know, things which may fill us with fear. But that is not true. In Christ, God has told us all that we need to know for His glory and our salvation. God's message in Christ is His last Word because it is also His final Word.