1 John 2:6 says, He that saith he abideth in him ought himself also so to walk, even as he walked. John tells us that people who profess to put their faith in Jesus Christ should walk as He walked. It is not enough to just say we believe in Jesus Christ if we continue to walk, or live, by the standards of the world.
Verse seven adds, Brethren, I write no new commandment unto you, but an old commandment which ye had from the beginning. The old commandment is the word which ye have heard from the beginning. John said he wasn't writing a new commandment but a commandment that they had heard from the beginning. Jesus Christ was not an afterthought as a way to salvation but has been the only way from the beginning. Even when people were under the law looking ahead to the coming of Jesus Christ, they weren't saved by the law but by faith in God.
Verse eight continues, Again, a new commandment I write unto you, which thing is true in him and in you: because the darkness is past, and the true light now shineth. John then said he was writing a new commandment to those who had put their faith in Jesus Christ. This was not a commandment for all people, but only for those redeemed by faith in Jesus Christ.
Verse nine states, He that saith he is in the light, and hateth his brother, is in darkness even until now. This new commandment was one that Jesus Christ had given, and that is that we are to love our brother as ourselves. John said that if we profess to live in the light of God and don't love our fellow man, then we are still in darkness. We are to love others as Jesus did, being willing to lay down our lives for them to be saved, and this applies to all people. Jesus died even for those who were crucifying Him, and this is the love that we as Christians need to have for others.
Verse ten adds, He that loveth his brother abideth in the light, and there is none occasion of stumbling in him. John said that if we love our brothers that we live in the light and there is no reason for stumbling in our faith if we do.
Verse eleven continues, But he that hateth his brother is in darkness, and walketh in darkness, and knoweth not whither he goeth, because that darkness hath blinded his eyes. John then said that the opposite was true. If we hate our brothers, then we live in darkness and we don't know where we are going spiritually. We cannot profess to love God while hating other people at the same time. If we hate others, God's light no longer guides us.