Psalm 9:10 (NKJV)
And those who know Your name will put their trust in You; For You, Lord, have not forsaken those who seek You.
I was reading this verse this morning and was reminded of the famous question "What about those who have never heard of Gospel, how can they be saved?" Romans 1:20 says that God's creation clearly testifies of a Creator showing us his power and attributes. So there is no excuse for not believing in God. But how would someone who had never heard the Gospel ever get saved? This verse in Psalm 9:10 tells that those who seek Him will never be forsaken. Our problem is not how can we know God but rather that we do not act upon what is already known about Him!
Jeremiah 29:13 (NKJV)
And you will seek Me and find Me, when you search for Me with all your heart.
On the other hand, there are those who claim to know him but have never really sought him. They are interested in wearing the label and having the benefits but they are not really going after God because they do not really care about what He says as evidenced by their lack of obedience.
Matthew 7:21 (NKJV)
Not everyone who says to Me, "Lord, Lord," shall enter the kingdom of heaven, but he who does the will of My Father in heaven. Many will say to Me in that day, "Lord, Lord, have we not prophesied in Your name, cast out demons in Your name, and done many wonders in Your name?" And then I will declare to them, "I never knew you; depart from Me, you who practice lawlessness!"