We borrow from David and Solomon to expand on the meaning of Johns passage. The Bible is one all inclusive set of standards and policy and truth from God. You cannot extrapolate one meaning from one passage and another meaning from another passage. All doctrine has to be viewed in one light and in one consistent pattern.
John is demonstrating the pattern of thought form the believer who has hate in his heart. Hate is a broadly defined set of sins which is driven by many other sins including envy, jealousy, lust, frustration, paranoia, and many others, and can lead to various types of sins like complaining, gossip, revenge, violence and so forth.
5 They do not know nor do they understand; They walk about in darkness; NASB
14 The wise man’s eyes are in his head, but the fool walks in darkness. And yet I know that one fate befalls them both. NASB
John is using two contrasting terms to demonstrate that your attitude in life is driven by what you have in your soul. If you have doctrine, then your attitude will be more tolerant than if you lack doctrine in your soul.
But furthermore, your attitude is also related to where you live spiritually. You can live your life in fellowship (in the light) or you can live your life out of fellowship (in the darkness). The two are mutually exclusive. You cannot have your life both ways. You cannot have a little sin with your goodness.
Contrary to popular opinion, sin is not the spice of life, nor is living out of fellowship give you a little more fun in life. The only way to have a great life, is to life in fellowship, and function within that sphere. To the positive believer, all good things come. That includes fun.
Where life is agreeable to a dark mind and conscience, then the negative believer doesn’t know where he is going, and he doesn’t know where his darkened soul is carrying him.
Where that darkness dwells (out of fellowship), the mind, the judgment, and the conscience will be darkened and the discernment of life will fade into a miserable life.