This dissertation contends that interpreters have underestimated assurance of salvation in the Letter to the Hebrews and the author's confidence in his recipients' salvation. Chapter 1 considers the history of research, examining how several recent commentators and interpreters have understood the warnings and assurance in the letter. Special attention is given to their interpretation of the perfection of believers and the new covenant promises, as well as the author's confidence, God's promise, and the believer's hope in Hebrews 6:9-20. Chapter 2 examines the concept of perfection in Hebrews--with respect to Christ and believers--and specifically considers its relationship to the promises of the new covenant as prophesied in Jeremiah 31, quoted in Hebrews 8:8-12 and 10:16-17. I analyze several relevant texts, including 3:7-4:13; 7:11-28; 8:1-13; 9:1-10; 10:1-18, 22; 11:39-40; 12:18-24; and 13:20-21, and consider implications for assurance of salvation. Chapter 3 provides an exegetical analysis of Hebrews 6:9-20, seeking to understand the author's confidence in the recipients and the contribution the passage makes to assurance of salvation in Hebrews. Chapter 4 offers an explanation of the warnings of Hebrews that can account for the findings of chapters 2 and 3. I consider and evaluate the three most common interpretations of the warnings: the loss-of-rewards view, the false-believer view, and the loss-of-salvation view. Building on this, I present the "means-of-salvation" view, responding to criticisms of the view and demonstrating how it best integrates the warnings with the passages and themes that promote Christian assurance. Thus, I defend the thesis that interpreters of Hebrews have greatly underestimated assurance of salvation in the letter (1) by demonstrating that the author implicitly affirms his readers can have assurance of salvation in light of the sacrificial work of Christ and (2) by demonstrating that the means-of-salvation view offers the best means of integrating assurance of salvation with the warnings against Christian apostasy in the letter.