What happens when the apostles begin to fade? When miracles are not central? When persecution intensifies? When believers must live by unseen conviction? This is where Hebrews enters.
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• Hebrews 11:1 (NIV) – Bible Gateway
  “Now faith is confidence in what we hope for and assurance about what we do not see.”
• Hebrews 11:6 (NIV) – Bible Gateway
  “And without faith it is impossible to please God, because anyone who comes to him must believe that he exists and that he rewards those who earnestly seek him.”
• Hebrews 11:35 (NIV) – Bible Gateway
  “There were others who were tortured, refusing to be released so that they might gain an even better resurrection.”

F. F. Bruce – Former Rylands Professor, University of Manchester

“The readers had already suffered for their confession, and the author urges them not to abandon the ground they had gained.”, Enduring Word Commentary on Hebrews

Ben Witherington III – Professor of New Testament, Asbury Theological Seminary

“Hebrews calls its audience to public perseverance, not private belief alone.”, Ben Witherington Resources

Michael S. Heiser, Ph.D. – Biblical scholar and author with expertise in ancient Hebrew and Semitic languages; taught on Hebrews in The Naked Bible Podcast indicating the book’s themes of faith and endurance. Transcript: Naked Bible Podcast, Episode 182: Hebrews 4:1‑13

Ron Rhodes, ThM – Evangelical Theological Seminary

Highlights the “not shrink back” principle as an anchor for believers under empire. Ron Rhodes Biblical Commentary

• 1 Clement (Letter to Corinth, c. AD 96) – Early Christian Writings
  Describes believers contending unto death; early post-apostolic endurance
• Shepherd of Hermas, Vision 3 (2nd century) – Early Christian Writings
  Believers tested like stones before being fitted into a tower; metaphor for endurance under trial
• Ignatius of Antioch (Letters, c. AD 107) – Early Christian Writings
  

Early Christian Torture: https://listverse.com/2013/09/24/10-horrifying-tortures-of-early-christians/
Not all references are listed due to character limits.