John 17:3: And this is life eternal, that they might know thee the only true God, and Jesus Christ, whom thou hast sent.
The passage does not just say that we should know about God. We must know Him personally and intimately. Unless we know Him personally we do not have eternal life. When we know God we will know that He loves us and that His commandments are for our benefit and we will want to please Him more and more, we will learn and understand His commandments, we will want to live different (sanctified) lives and we will fight to abstain from sin. Individuals who have no interest in living separate and honorable lives do not know Him. Not knowing God and not knowing how to abstain from sin are the most destructive forms of ignorance known to men.
1 Thessalonians 4:1: Furthermore then we beseech you, brethren, and exhort you by the Lord Jesus, that as ye have received of us how ye ought to walk and to please God, so ye would abound more and more. 2 For ye know what commandments we gave you by the Lord Jesus. 3 For this is the will of God, even your sanctification, that ye should abstain from fornication: 4 That every one of you should know how to possess his vessel in sanctification and honour; 5 Not in the lust of concupiscence, even as the Gentiles which know not God:
1 John 5:3: For this is the love of God, that we keep his commandments: and his commandments are not grievous.
Deuteronomy 6:18a: And thou shalt do that which is right and good in the sight of the LORD: that it may be well with thee, . . .
2 Thessalonians 1:7: And to you who are troubled rest with us, when the Lord Jesus shall be revealed from heaven with his mighty angels, 8 In flaming fire taking vengeance on them that know not God, and that obey not the gospel of our Lord Jesus Christ:
Proverbs 1:7: The fear of the LORD is the beginning of knowledge: but fools despise wisdom and instruction.
Proverbs 9:10: The fear of the LORD is the beginning of wisdom: and the knowledge of the holy is understanding.
Those who do not know God know nothing of eternal or spiritual value. They know nothing of what God wants them to know and nothing of what they need most to know.
Job 8:9: (For we are but of yesterday, and know nothing, because our days upon earth are a shadow:)
1 Corinthians 4:4: For I know nothing by myself; yet am I not hereby justified: but he that judgeth me is the Lord.
1 Corinthians 8:2: And if any man think that he knoweth any thing, he knoweth nothing yet as he ought to know.
Proverbs 9:13: A foolish woman is clamorous: she is simple, and knoweth nothing.
Vance Havner said that there are some who not only don*t know anything, they don*t even suspect anything.