Begin with the priestly argument surrounding the verse. Hebrews describes Christ appearing to remove sin through His sacrifice, appearing before God on our behalf, and appearing a second time for the salvation of those awaiting Him (Hebrews 9:24–28). The same Lord acts throughout, and His offering is sufficient.
The second appearing is expressly distinguished from bearing sin. Christ does not return to offer Himself again or repair an inadequate atonement. Hebrews has already described His entrance into the true sanctuary through His own blood and His obtaining eternal redemption (Hebrews 9:11–14).
The Day of Atonement supplies an important background. The people awaited the priest’s emergence after his ministry within the sanctuary. Read within that pattern, Christ’s appearing manifests the saving efficacy of His completed work. The word second alone does not explain the whole promise; the surrounding priestly argument gives it substance.
In the covenantal reading developed here, the disappearance of the obsolete temple order publicly disclosed that Christ’s heavenly ministry had decisively surpassed it (Hebrews 8:6–13). We relate that historical manifestation to AD 70. This is an interpretation drawn from the letter’s argument, rather than a calendar date stated in Hebrews 9:28 or a literal reenactment of an earthly priest’s movements.
The assurance reaches your life now. Christ’s sacrifice does not await completion before you can approach God. Hebrews calls believers to draw near because the way has already been opened (Hebrews 10:12–22).
Scripture in this answer
Hebrews 8:6–13; 9:11–28; 10:12–22