The image of light, to which the fourth Gospel refers Jesus (cf. Jn 8:12), is now applied to God, the source of revelation and holiness. Each of the expressions introduced by this phrase: “If we say” (6:8, 10) reflects the sentiment of the Gnostic opponents, whose teachings St. John opposes. Truth is the Word of God, proclaimed by Jesus (8:10), which penetrates the believer until it transforms his life. “Acting sincerely” points the way to a vital encounter with Jesus.
The apostle insists with healthy realism: we are sinners. Sin exists (8:10). The heartfelt awareness of our sin should not lead us to despair but to renew our faith in Christ. He is notably emphasized with three salvific roles. He is our “Advocate”—Parakletos. In the Gospel, this refers to the Holy Spirit (cf. Jn 14:16, 26), but here it pertains to Jesus Christ, who intercedes for us in God’s court. He is “Just,” more in the manifestation of his salvation work than in his essence, since he forgives and justifies sinners. He is the “Victim” of atonement (cf. Ex 29:36ff), pointing to Christ’s voluntary sacrifice on the cross (cf. Rev 5:9ff), which has everlasting and universal effectiveness.