God created us in His own image to have an abundant life.
He didn't make us robots to automatically love and obey Him. God gave us a will and freedom to choose. We chose to
disobey God and go our own willful way. We still make this choice today. The result is separation from God. Why? God is Holy and untainted by sin. He is perfect in His behavior. People are sinful because they are born in sin and choose to sin.
The Bible says...
"For all have sinned and fall short of the glory of God." Romans 3:23
"For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord." Romans 6:23
"But your iniquities have separated you from your God; And your sins have hidden His face from you, so that He will not hear." Isaiah 59:2
So...how do we fix it?
It was our choice.