This is a faithful saying, and worthy of all acceptation, that Christ Jesus came into the world to save sinners; of whom I am chief. 1 Timothy 1:15
For then must he have suffered since the foundation of the world: but now once in the end of the world hath he appeared to put away sin by the sacrifice of himself. Hebrews 9:26
In Christ's first coming, He implemented a rescue plan conceived in the mind of God before the foundation of the world. He did not come to promote holiday cheer, boost end-of-year sales, or serve as the central figure in a nativity scene. He came to save sinners.
To save sinners, Christ had to put away what makes people sinners - namely, sin. At the dawn of man's history, sin, like an unwelcome virus, infected mankind early enough. But how could it be exterminated? God was already answering this question through the Old Testament sacrificial system. One of the main themes in the epistle to the Hebrews is the repetitious labors of the Old Testament priests. "And they truly were many priests, because they were not suffered to continue because of death" (Heb. 7:23) Morning and evening, priests placed burnt offerings for sin on an altar, the fire of which was never to go out (2 Chron. 13:11; Lev. 6:12).
Nonetheless, sins were not fully, extinguished through this system (Heb. 10:4). Old Testament sacrifices were merely a shadow, or copy of what was to come (Heb 9:23); thus, the priesthood of Aaron could have sacrificed burnt offerings for a million years without putting away a single sin. The writer of Hebrews says the seed of Adam needed a better priesthood to put away sins - a priesthood "after the order of Melchisedec" (Heb. 7:17; cf. Ps. 11-:4). Likewise, a better sacrifice offered in a better tabernacle was necessary. When a truly perfect sacrifice was offered in the tabernacle of heaven, sin would finally be put away…
Christ put away the sins of many first by carrying them to the cross, and then to the grave (Heb. 9:28). The sins of God's people were crucified and buried in Christ (Rom. 6:4-5). So fully has Christ purged the believer's sins that Hebrews 9:28 adds, "Unto them that look for him shall he appear the second time without sin unto salvation." How staggering is the thought that we can eagerly anticipate the return of the Savior who was wounded of our transgressions!
Why Christ Came: 31 Meditations of the Incarnation, Joel R. Beeke & William Boekestein, Reformation Heritage Books, 2013, pp. 5-6.