From A.W.Pink;
"Hath He appeared to put away sin by the sacrifice of Himself." He "appeared" here on earth (the Greek word is quite different from the one used in verse 24): of old He had been obscurely shadowed forth in types, but now He was "manifest in flesh" (1 Tim. 3:10). The end or purpose of this appearing of Christ was to "put away sin"—the Greek word is a very strong one, and is rendered "disannuling" in Hebrews 7:18. Let it be carefully noted that this declaration is made only as it respects the Church of Christ. He made a complete atonement for all the sin of all His people, receiving its wages, expiating its guilt, destroying its dominion. The results are that, when God applies to the penitent believer the virtues of Christ’s sacrifice, all condemnation is removed (Rom. 8:1), and its reigning power is destroyed (Rom. 6:14).
"So Christ was once offered." As the death-sentence, as a penal infliction, was passed upon all of Adam’s descendants (Rom. 5:12) viewed as criminals, as having broken the law in the person of their federal head, so Christ was "appointed" or sentenced by God, the Judge of all, to undergo the curse of the law, on the behalf and in the stead of those whom He represented. "So Christ was once offered to bear the sin of many." Here we see that deliverance from the curse which the wisdom and grace of God provided for His elect. The Anointed One, as the High Priest of His people, presented to God an all-sufficient and final satisfaction for all the sins of all who have been, from eternity, given to Him by the Father. Thus verses 27, 28 present the antithesis of the Law and the Gospel, as it relates to "men" indefinitely, and to the "many" specifically. The sins of many He "bare"—had imputed to Him, received the punishment of, and fully expiated—in His own body on the tree (1 Pet. 2:24).