1 John 1:7 (ESV) … “But if we walk in the light, as he is in the light, we have fellowship with one another, and the blood of Jesus his Son cleanses us from all sin.”
The counterhypothesis is also expressed in the form of a conditional sentence, which begins: But if we walk in the light, as he is in the light.… In 1:5 the author said, ‘God is light’, but here he says that God ‘is in the light’, which indicates that he is going to use the metaphor in an ethical fashion. A situation is now projected which is opposite to the one projected in 1:6. Here he is speaking of people who walk in the light, as God is in the light. What it actually means to ‘walk in the light’ and to ‘walk in the darkness’ is not explained in this letter. Probably the best explanation of what it means is to be found in the Fourth Gospel:
And this is the judgment, that the light has come into the world, and people loved darkness rather than light because their deeds were evil. For all who do evil hate the light and do not come to the light, so that their deeds may not be exposed. But those who do what is true come to the light, so that it may be clearly seen that their deeds have been done in God. (John 3:19–21, NRSV)
This suggests that ‘walking in the light’ involves a willingness to be open towards God and his revelation in Christ, while ‘walking in the darkness’ involves a refusal to do this. The author of 1 John, however, is less concerned to define what walking in the light or the darkness means than he is to explain the consequences of doing so. As noted in the commentary on 1:6, the consequences of walking in the darkness while claiming fellowship with God are that ‘we lie and do not live by the truth’. The consequences of walking in the light are spelled out in 1:7. These are twofold:
The first consequence is, we have fellowship with one another. As people walk in the light with God, they have fellowship with one another. This statement comes as something of a surprise. We might expect the consequence to be that people who walk in the light would have fellowship with God. After all, that is what is denied to those who walk in darkness. However, the author says the first consequence is that we have fellowship with one another. This is not to say that those who walk in the light do not have fellowship with God, but rather to assert that those who do have fellowship with God as they walk in the light will also have fellowship with one another. Or, to put it another way, there is no real fellowship with God which is not expressed in fellowship with other believers. It would appear from what is to come later in this letter that this unexpected statement about the consequence of walking in the light is made to rule out the claim of the secessionists who say they do have fellowship with God while not sharing fellowship with other believers (in this case, with those of the author’s persuasion).
The second consequence is the blood of Jesus, his Son, purifies us from every sin. As people walk in the light with God, the blood of his Son Jesus ‘purifies’ them from their sins. When the author speaks of the ‘blood of Jesus’ he is referring to his violent death on the cross, and it is this death which provides purification18 from sins for those who walk in the light with God. By his use of the present tense for the verbs ‘to walk’ and ‘to purify’, the author represents both the walking and the cleansing as ongoing activities. One lesson that may be learned from this second consequence is that walking in the light does not mean that those who do so never sin, but that they do not seek to hide that fact from God. They ‘walk in the light’ with him, and the result of their doing so is that the blood of his Son Jesus purifies them from their sins. Purification from sin, when unpacked, is virtually equivalent to forgiveness of sins, as the use of these two concepts in parallel in 1:9 indicates (the two concepts are also found in parallel in Jer 33:8: ‘I will cleanse them from all the sin they have committed against me and will forgive all their sins of rebellion against me’). That the concomitant of walking in the light is being purified from every sin suggests that walking in the darkness might best be interpreted here, not simply as walking in ignorance, but as walking in sin.