The person who says, "I have come to know Him," but does not obey what He commands, is lying [by such a profession], and the truth [about the matter] is not in his heart.

He is

If we claim to share a relationship with God and yet live in darkness [i.e., in a sinful way], we are lying and are not living a truthful life.

Jesus said to them, "If you were [really] blind [i.e., unable to see spiritually], you would not be guilty of sin. But since you claim, 'We can see [fine],' you remain guilty of sin."

if you know His will and have been taught by the law of Moses to [evaluate and] give approval to what is best;

And hateth

So, do not be surprised, brothers, if the people of the world hate you.

Is in

But the person who hates his brother is in the darkness [of sin] and he lives in [harmony with] that darkness, and he does not know where he is heading, because the darkness [of sin] has blinded his eyes [to his spiritual condition].

If I have the ability to speak in the languages of human beings and angels [Note: Perhaps the idea is supernaturally and eloquently], but do not have love [for people], I have become [no more than] a noisy gong or a clanging cymbal.

But, anyone who lacks these qualities is [spiritually] blind and shortsighted, and has forgotten that he has been cleansed [i.e., forgiven] of his past sins.

General references

My commandment [to you] is this: You should love one another just as I have loved you.

Continue to love [one another] as brothers.