John wrote, “My little children, I am writing you these things so that you may not sin. But if anyone does sin, we have an advocate with the Father—Jesus Christ the righteous one. He himself is the atoning sacrifice, for our sins, and not only for ours, but also for those of the whole world” (1 John 2:2). John is referencing the doctrine of atonement. Within the subject of atonement is the doctrine of propitiation. What is the doctrine of propitiation? How does it apply to the Christian?
John Stott beautifully summarized the doctrine of propitiation:
the propitiatory offerings were divinely instituted and prescribed as the means by which the sinner might be forgiven. ‘The life of a creature is in the blood, and I have given it to you to make atonement for yourselves on the altar …’ (Lev. 17:11). The sacrifices were not a human arrangement, but a divine gift. So with the sacrifice of Christ. God gave his Son to die for sinners. This gift was not only the result of God’s love (John 3:16), nor only the proof and pledge of it (Rom. 5:8; 8:32), but the very essence of it: ‘This is love … that he loved us and sent his Son as an atoning sacrifice for our sins’ (1 John 4:10).
Before we can go on to see how propitiation stands in respect to “us” and to “the whole world,” we need to know what propitiation is. The standard Greek Lexicon of our day states that propitiation (ἱλασμός) is “appeasement necessitated by sin” This Greek word is only used twice in the New Testament (1 John 2:2 and 4:10). The Septuagint used the word “ἱλασμός” to translate Hebrew words that had to do with “atonement” (Lev. 25:9; Num. 5:8), and the sin offering of Ezekiel 44:27.
When we move to study the concept from the standpoint of Biblical Theology, then we see that this theme runs throughout the Biblical narrative. The Mosaic system was filled with sacrifices whose blood was shed to cover the sins of the people. These sacrifices anticipated the Sacrifice which God made of himself for himself on behalf of the people. So Hebrews looks back to the inabilities of the Old Testament sacrifices to highlight the excellencies of Jesus’ sacrifice of himself (Hebrews 10:1-10). The book of Revelation holds Jesus up as the Lamb that has been slain. The 24 elders sang, “You are worthy to take the scroll and to open its seals, because you were slaughtered, and you purchased people for God by your blood from every tribe and language and people and nation. You made them a kingdom and priests to our God and they will reign on the earth” (Rev. 5:9-10). Biblical theology has given us a picture of sacrificial atonement which is manifested in Christ’s own sacrifice at Calvary.
Graduating to systematic theology, we see that the sacrifice of Christ was necessary because God is holy, his people are cursed by sin, and our merciful and loving God wants to make salvation from sin possible. Punishment for sin is necessary because sin must be punished. If God did not punish sin, then he would be unjust. Sin must be punished to maintain God’s righteousness, his holiness, his truthfulness, and his love. Christ, then becomes the lightning rod of all these divine attributes. Sin is punished in his flesh so that sinners might go free. God’s holiness is maintained because the sins of his people are covered in the blood of Jesus. His love is preeminently on display in Christ’s willing sacrifice. Penal substitutionary atonement is vital to the understanding of Biblical Theology and Systematic Theology if we are going to be honest with the Sacred Text. It may not fit with modern thought, but it is the revelation of God’s eternal thought. You must choose which to follow.
 John R. W. Stott, The Letters of John: An Introduction and Commentary, vol. 19, Tyndale New Testament Commentaries (Downers Grove, IL: InterVarsity Press, 1988), 92.
 William Arndt et al., A Greek-English Lexicon of the New Testament and Other Early Christian Literature (Chicago: University of Chicago Press, 2000), 474.