Summary: The person that knows God will give an experimental taste and relish of the goodness of God, that God is good but a fool will hinder his own proficiency in the knowledge of God to enable him do evil to his satisfaction.
BELIEVING IN GOD YET NOT KNOWING HIM
" Whoever does not love does not know God, because God is love." ( 1 John 4:8)
Behold, God is exalted, and we do not know Him; The number of His years is unsearchable.
It is a great thing to know God. Blessed are those who knows God, they will walk in His statutes and obey His commandments. Blessed are those who knows the Lord of Hosts; who command all heavenly, earthly and satanic forces. What a great privilege and grace to know the Almighty God, who does marvelous things without number ! (Job 5:9)
The fool says in his heart, "There is no God." “Your dwelling is in the midst of deceit; through deceit they refuse to know Me,” declares the Lord.(Jeremiah 9:6) What a great tragedy that befall such fool! He refuse to accept the being of Almighty God nor His works. Even the heavens declare the glory of God; and the firmament shows His handiwork. The earth belongs to Him , and everything that dwells therein. He created everything and the fool couldn't acknowledge God's providence.
There is no excuse for not believing in God because of the testimony of creation (Romans 1) and the testimony of conscience (Romans 2). People intuitively know what is right and wrong: do not murder, do not steal, do not commit adultery, honor parents… ... Because “God has written His law on our hearts”.
No wicked man knows God, and every man that doesn't know God is wicked.
Many people who believe in God are so occupied with their daily activities that they neglect to serve Him.
IGNORANCE IS NO EXCUSE
The eternal power and deity of God are observed by all. "For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who suppress the truth in unrighteousness, because what may be known of God is manifest in them, for God has shown it to them. For since the creation of the world His invisible attributes are clearly seen, being understood by the things that are made, even His eternal power and Godhead, so that they are without excuse, because, although they knew God, they did not glorify Him as God, nor were thankful, but became futile in their thoughts, and their foolish hearts were darkened" (Romans 1:18-21).
We will briefly look at the categories of people who acknowledge the existence of God but refuse to know Him:
1. TOTAL IGNORANCE OF GOD
The person who has no light of the knowledge of God must be wicked and walk in darkness.
2. FALSE /ERRONEOUS KNOWLEDGE OF GOD
Wrong knowledge is a kind of ignorance. God has declared himself to be known, yet they don't know Him. Those who have total ignorance of God(who are in total darkness) as well as those who have an unsound knowledge(who are in false light) are numbered with the wicked. Those who have false principles cannot have a right frame of heart towards God. "Pour out Your wrath upon the nations which do not know You, and upon the kingdoms which do not call upon Your name" (Psalm 79:6)
3. PRACTICAL IGNORANCE OF GOD
They know God but act contrary to their knowledge of Him, they have a right notion and their understanding is not wrapped up in error. " They claim to know God, but by their actions they deny him. They are detestable, disobedient and unfit for doing anything good." (Titus 1:16). This knowledge is practical ignorance.
"But these speak evil of those things which they know not: but what they know naturally, as brute beasts, in those things they corrupt themselves." (Jude 10). They do not live according to natural principles, as they speak evil of things they do not know, and do evil in those things which they know. Their knowledge is according to the light of nature, but their actions are against the light of nature. They know things as beast do, naturally, but they act contrary to this knowledge; beasts don't do this. Now as wicked man corrupts himself in those things that he knows by nature, so he may corrupt himself in that which he knows by doctrine or instruction. He is brutish in his knowledge (Jeremiah 10:14) though he have a higher knowledge than a beast. To have notions according to knowledge, and actions according to ignorance , is to be brutish in knowledge.
"Awake to righteousness, and sin not; for some have not the knowledge of God: I speak this to your shame." (1 Corinthians 15:34) - This speaks to those who have erroneous knowledge of God, or rather, of those that live in ways of unrighteousness against their knowledge. They don't have the knowledge of God that keeps them to the rule of righteousness. This is a practical ignorance of not knowing God.