Book of 1 John Chapter 2 Vs. 9

 The New Commandment

1 John 2:9 “He that saith he is in the light, and hateth his brother, is in darkness even until now.”

He that saith... No man professing a Christian experience who hates his brother has received a saving knowledge of truth (1Jhn. 2:9, 2:11).

This is just saying, those who hate others are not walking in the Light. The perfect Light provided for believers leads us into His perfect love. It does not allow hate of any kind. Hate is of the devil and is surrounded by darkness.

Hateth (μισῶν)

The sharp issue is maintained here as in Christ's words, He that is not with me is against me (Luke 11:23). Men fall into two classes, those who are in fellowship with God, and therefore walk in light and love, and those who are not in fellowship with God, and therefore walk in darkness and hatred. A direct opposition says Bengel; where love is not, there is hatred. The heart is not empty. See John 3:20; 7:7; 15:18 sqq.; John 17:14. The word hate is opposed both to the love of natural affection φιλεῖν, and to the more discriminating sentiment - love founded on a just estimate ἀγαπᾶν. For the former see John 12:25; 15:18, 15:19; compare Luke 14:26. For the latter, 1Jhn. 3:14, 3:15; 4:20, Mat. 5:43; 6:24; Eph. 5:28, 5:29. In the former case, hatred, which may become a moral duty, involves the subjection of an instinct. In the latter case it expresses a general determination of character (Westcott).

Doctrinal truth about spiritual matters means nothing without compassion for others. For John, hateth seems to mean simply fails to love.

In the original language, hate coveys the idea of someone who habitually hates or is marked by a lifestyle of hate.

His brother (τὸν ἀδελφόν)

His fellow-Christian. The singular, brother, is characteristic of this Epistle. See 1Jhn. 2:10, 2:11; 3:10, 3:15, 3:17; 4:20, 4:21; 5:16. Christians are called in the New Testament, Christians (Acts 11:26; 26:28; 1Pet. 4:16), mainly by those outside of the Christian circle. Disciples, applied to all followers of Christ (John 2:11; 6:61) and strictly to the twelve (John 13:5 sqq.). In Acts 19:1, to those who had received only John's baptism. Not found in John's Epistles nor in Revelation. Brethren. The first title given to the body of believers after the Ascension (Acts 1:15, where the true reading is ἀδελφῶν brethren, for μαθητῶν disciples). See Acts 9:30; 10:23; 11:29; 1Thes. 4:10; 5:26; 1Jhn. 3:14; 3Jhn. 1:5, 1:10; John 21:23. Peter has ἡ ἀδελφότης the brotherhood (1Pet. 2:17; 5:9). The believers. Under three forms: The believers οἱ πιστοί; Acts 10:45; 1Tim. 4:12; they that believe οἱ πιστεύοντες; 1Pet. 2:7; 1Thes. 1:7; Eph. 1:19); they that believed οἱ πιστεύσαντες; Acts 2:44; 4:32; Heb. 4:3). The saints οἱ ἅγιοι; characteristic of Paul and Revelation. Four times in the Acts (Acts 9:13, 9:32, 9:41; 26:10), and once in Jude (Jude 1:3). Also Heb. 6:10; 13:24. In Paul, 1Cor. 6:1; 14:33; Eph. 1:1, 1:15, etc. In Rev. 5:8; 8:3, 8:4; 11:18, etc.

Is in the darkness even until now: Those who profess to be Christians, yet are characterized by hate, demonstrate by such action that they have never been born again. The false teachers made claims to enlightenment, transcendent knowledge of God, and salvation, but their actions, especially the lack of love, proved all such claims false (see also verse 11).

Until now (ἕως ἄρτι)

Though the light has been increasing, and though he may claim that he has been in the light from the first. The phrase occurs in John 2:10; 5:17; 16:24; and is used by Paul, 1Cor. 4:13; 8:7; 15:6.

It follows that anyone who claims to be in the light but hates his brother is still in the darkness. This warning is clearly intended for Christians as the words his brother plainly show. An unsaved person can indeed hate a brother of physical kin, but since he has no spiritual kin, he cannot really hate his (spiritual) brother. If John thought that no Christian could hate another Christian, there was no need to personalize the relationship with the word his. But the opinion, held by some, that a true Christian could never hate another Christian is naive and contrary to the Bible and experience. Even so great a man as King David was guilty of murder, which is the final expression of hate. John was warning his readers against a spiritual danger that is all too real (cf. 1Jhn. 1:8, 1:10). And he was affirming that a Christian who can hate his fellow Christian has not genuinely escaped from the darkness of this present passing Age. To put it another way, he has much to learn about God and cannot legitimately claim an intimate knowledge of Christ. If he really knew Christ as he ought, he would love his brother.