We are from God, and whoever knows God listens to us; but whoever is not from God does not listen to us. This is how we recognize the Spirit of truth and the spirit of falsehood (1 John 4:6).

Two kinds of spirit are working in this world: one is "the Spirit of truth," which comes from God, and the other is "the spirit of falsehood," which comes from Satan. The former is the spirit of life, light and love, and the latter is the spirit of death, darkness and hatred. All humans belong either to the Spirit of truth or to that of falsehood.

If we claim to have fellowship with him yet walk in the darkness, we lie and do not live by the truth (1:6).

To "have fellowship with him (God)" means to know him and to love him, and anyone who has such fellowship walks in the light and loves his brother. In contrast, anyone who walks in the darkness hates his brother, and even if he claims to have fellowship with God, he belongs to the spirit of falsehood, and the truth is not in him.

Anyone who claims to be in the light but hates his brother is still in the darkness. Whoever loves his brother lives in the light, and there is nothing in him to make him stumble (2:9-10).

It is important to keep in mind that the whole letter is about the command to love one another. With different words and expressions, the author is not only repeatedly encouraging the readers to love as a command, but also explaining how reasonable, logical and realistic it is for those who were born of God to do so.

If anyone says, "I love God," yet hates his brother, he is a liar. For anyone who does not love his brother, whom he has seen, cannot love God, whom he has not seen (4:20).

Note the expression, "if anyone says (claims)…, yet (but) …" (also in 2:4 and 9), by which he is speaking of the hypocritical attitude of antichrists: they are led by the spirit of falsehood, and do not have fellowship neither with the believers nor with God himself.

For Christians today, to love one another is usually considered something that is optional, extra, or additional to not sinning: "if you want to love, you can do so, but if you do not want to, you do not need to." In other words, to hate is a sin, but it is quite permissible to not love actively and deeply, or to be indifferent to the needs of others.

This is how we know who the children of God are and who the children of the devil are: Anyone who does not do what is right is not a child of God; and (such is) the one who does not love his brother (3:10).

"Anyone who does not do what is right" is "the one who does not love his brother," and such a man is "not a child of God." It does not refer to hatred only, but not to love actively with the attitude of indifference is included.

This is how we know what love is: Jesus Christ laid down his life for us. And we ought to lay down our lives for our brothers (v. 16).

Did Christ go on to the cross and die for us with the passive kind of love? John also says:

If anyone has material possessions and sees his brother in need but has no pity on him, how can the love of God be in him (v. 17)?