25 God presented Christ as a sacrifice of atonement, through the shedding of his blood—to be received by faith. He did this to demonstrate his righteousness, because in his forbearance he had left the sins committed beforehand unpunished—
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3:25 sacrifice of atonement, through the shedding of his blood. Paul speaks literally here of the mercy seat, the place of propitiation, annually consecrated to God by sacrificial blood. Both ancient Israel and its milieu understood principles of propitiating, or appeasing, a deity’s wrath (cf. 1:18) as well as of cleansing impurity. To emphasize this, atonement through Jesus’ shed blood depicts Jesus as a sacrifice (cf. 5:9; 8:3). Some Jewish people already recognized that martyrdom could turn away God’s wrath from his people (4 Maccabees 17:22); early Christians regarded Jesus’ death as a special category. left the sins committed beforehand unpunished. God had graciously “passed over” (cf. Ex 12:13) sins before the time of the cross.
2 He is the atoning sacrifice for our sins, and not only for ours but also for the sins of the whole world.
2 Our advocate does not maintain our innocence but confesses our guilt. Then he enters his plea before the Father on our behalf as the one who has made "the atoning sacrifice for our sins" (this word also occurs in 4:10; cf. also Lk 18:13; Ro 3:25; Heb 2:17; 9:5). And his sacrifice is not only for our sins, "but also for the sins of the whole world." This statement asserts two things: Christ's sacrifice is sufficient for all, and it is necessary for all.
10 This is love: not that we loved God, but that he loved us and sent his Son as an atoning sacrifice for our sins.
10 The author now distinguishes agape love from any love claimed by the false teachers. It is not that "we loved God" (3:17; 4:20), as his opponents claimed, but that "he loved us." Agape love can be given to God only when it has first been received from God. It exists only as response to his initial love for us. Moreover, God's love for us defines what true love requires—the commitment to sacrifice one's most beloved possession for another's gain. So for God, love required that he send "his Son as an atoning sacrifice [see comment on 2:2] for our sins."
The difference in understanding between John and the false teachers is never greater than in their understanding of love. The false teachers claimed to love God but understood love not in Christian terms but in those of Greek philosophy. Love in the Hellenistic world became a mystical craving for union with the eternal. Two things derive from this understanding of love. First, love for God as expressed by the false teachers becomes primarily an exercise in self-gratification. Second, one can never attribute love to God and say, for example, that God loves us. God as the Absolute is always passionless and unmoved, according to them.