Why don't people know God as Father?
Because our relationship with God has been broken! We have wandered off from him and gone our own way.
Going our own way like this is called sin. It may be a deliberate rejection of God or, more often, simply ignoring him. Sin shows itself in many ways: in the wrong things we do and the negative things we feel.
Wrong actions usually starts out being attractive, but sooner or later sin inevitably hurts, spoils or destroys. Furthermore, sin becomes frightening for many people because it starts to take control and we find ourselves powerless to resist.
The most common negative emotion caused by sin is a feeling of emptiness. We were made to know God: without him there is a gap left in our lives that nothing else can fill. As a result many people feel their lives have no meaning or purpose.
We can try to fill this gap by other relationships, or by keeping busy, or by filling our lives with entertainment or thrills, or even with religious rituals. All these will fail to solve the real problem. We need to find our way back to a relationship with God as Father -- that is where the solution lies.
Point 3 explains what God has done to give us a second chance to know him.