By their attitude toward the atonement, theological systems classify themselves as pagan or Christian.
Their position on the atonement also reflects their idea of the nature of God, of His law, and of sin.
And he is the propitiation for our sins
The proper meaning of the word is that of reconciling, appeasing, turning away anger, rendering propitious or favorable. ... There are certain things which do not enter into the idea of propitiation. They are such as these: It does not change the fact that the wrong was done. ...It does not change God...It prepares the way for it on the part of God, but whether they for whom it is made will be disposed to accept it is another question.
And not for our’s only
Not only the sins of those who are Christians. It is sufficient for us; sufficient for all the world.
But also for the sins of the whole world
This is one of the expressions occurring in the New Testament which demonstrate that the atonement was made for all people, and which cannot be reconciled with any other opinion. If he had died only for a part of the race, this language could not have been used. The phrase, “the whole world,” is one which naturally embraces all people; is such as would be used if it be supposed that the apostle meant to teach that Christ died for all people; and is such as cannot be explained on any other supposition.
This passage, interpreted in its plain and obvious meaning, teaches the following things:
(1) That the atonement in its own nature is adapted to all people, or that it is as much fitted to one individual, or one class, as another;
(2) That it is sufficient in merit for all; that is, that if anymore should be saved than actually will be, there would be no need of any additional suffering in order to save them;
(3) That it has no special adaptedness to one person or class more than another; that is, that in its own nature it did not render the salvation of one easier than that of another.
Albert Barnes' Notes on the Bible
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Also for the sins of the whole world. Christ's advocacy is limited to believers (1Jn_2:1; 1Jn_1:7): His propitiation extends as widely as sin: note, 2Pe_2:1, "the whole world" cannot be restricted to the believing portion (cf. 1Jn_4:14 and 1Jn_5:19). 'Thou, too, art part of the world: thine heart cannot think, The Lord died for Peter and Paul, but not for me' (Luther).
Jamieson, Fausset, Brown
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So adequate is Jesus Christ as God’s atoning Sacrifice that the efficacy of His work extends not merely to the sins of Christians themselves, but also to the sins of the whole world. In saying this, John was clearly affirming the view that Christ genuinely died for everyone (cf. 2Co_5:14-15, 2Co_5:19; Heb_2:9). This does not mean, of course, that everyone will be saved. It means rather that anyone who hears the gospel can be saved if he so desires (Rev_22:17).
The Bible Knowledge Commentary
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For the whole world (peri holou tou kosmou). It is possible to supply the ellipsis here of tōn hamartiōn (the sins of) as we have it in Heb_7:27, but a simpler way is just to regard “the whole world” as a mass of sin (1Jn_5:19). At any rate, the propitiation by Christ provides for salvation for all (Heb_2:9) if they will only be reconciled with God (2Co_5:19-21).
Word Pictures in the New Testament (A. T. Robertson)
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For the sins of the whole world (περὶ ὅλου τοῦ κόσμου)
The sins of (A. V., italicized) should be omitted; as in Revelation, for the whole world. Compare 1Jo_4:14; Joh_4:42; Joh_7:32. “The propitiation is as wide as the sin” (Bengel). If men do not experience its benefit, the fault is not in its efficacy. Düsterdieck (cited by Huther) says, “The propitiation has its real efficacy for the whole world; to believers it brings life, to unbelievers death.” Luther: “It is a patent fact that thou too art a part of the whole world; so that thine heart cannot deceive itself, and think, the Lord died for Peter and Paul, but not for me.”
Vincent's Word Studies
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Ours only… whole world—The heart of our apostle is too expansive to limit the grace of the Redeemer to a select number. Christ is a race Redeemer, a world-Saviour. The interpretation that strives against language so rich to force a limit upon it, dishonours Christ and dishonours itself. ...In fact, the very purpose of John here is, to deny and repudiate a limited atonement. Beautiful and true are the words of Bengel: “So wide as sin extends does the propitiation extend.”
Daniel Whedon's Commentary