Beloved, I do not write a new command to you but an old command, which you have from the beginning. The old command is the word which you heard. 8 Yet I write a new command to you, which is true in him and in you, that the darkness is passing away and the true light already is shining. 9 The one who says he is in the light and is hating his brother is still in the darkness. 10 The one who is loving his brother remains in the light and there is no stumbling in him. 11 But the one who is hating his brother is in darkness and walks in darkness and does not know where he is going, because the darkness has blinded his eyes.
John begins this section be reiterating a command from Jesus but phrasing it in a new way, hence it is both and old command and a new command. John does not give the command here, instead he elaborates on the implications.
The Old Command are the words of Jesus, as John says that the Old Command is the “word which you heard.” In John’s theological vocabulary, the word is Jesus. Thus, all of Jesus’ words were one command (which later we will find out is love one another). The import of this command is to walk in the light and not in the darkness.
What is the darkness? John makes it very clear in the Fourth Gospel that the darkness is what is in the world, dominates the world, and can only be thrust away by Jesus (John 1:5, 9-10). The darkness is passing away not because sin no longer exists, rather it is passing away because Jesus defeated it once and for all on the cross. No longer need sin be feared by the believer, nor the world, since sin has been overcome.
At the same time, the darkness thrives in the world because so many still hate others when claiming not to. One cannot be a Christian, John states, if one hates his brother. Now this is certainly not limited to flesh and blood family, rather this refers to those who are of the household of God. Whoever hates a fellow believer cannot claim to be as believer since such a person is walking in darkness, in sin, and not in the light of Jesus Christ.
John is stressing the importance of living rightly along side believing rightly. It gains you nothing if you claim to love Jesus yet your heart and actions show the lie. No matter how hard people cling to their theology, their Bible, their church, it does nothing if their lives do not match their words. Christianity is not something mentally assented to, rather it is a lifestyle. The only faith that saves is a living faith, meaning a faith lived out.
Are you living out your faith? Do you worry more about your theology than your practice? Are you walking in Jesus right now? Make no mistake, Calvinist or Arminian, your theology will not save you if you have not lived your life for God after claiming to be in Him.