This is the biggest hurdle for most thoughtful people. Why could an all powerful, all loving God allow so much evil in the world?
To understand, you have to realize what He did for us. God gave us free will. Free will means we have the choice between good and evil. If we could only choose good, how would that be free will?
When you think of the issue of evil, consider the question framed much more accurately as: Why would an all powerful, all loving God create us with the ability to choose evil?
The answer is this: He did so because He loved us enough to give us the choice to love Him.
tell me more about this choicethanks, but no thanks
To avoid the issue of evil, God could have created robots. You can program a robot to do whatever you want. He could have had a wonderfully ordered, always perfect universe. The robots would have recited prayers at the appropriate times, never misbehaved, always been good to each other, given thanks for everything they received and generally paid Him all the homage He could ever ask for.
If this was what God was interested in, robots would make a lot more sense. It is apparent from His actions, though, that God is much more interested in us for relationship than religion. Think about that old quote about loving something and setting it free. You cannot force someone to love you. They must, of their own free will, choose to do so. Anything less is not love.
If God desired a loving relationship with us, the only way He could do that would be to 'set us free'. Unfortunately, setting us free has resulted in the world we see today. Should we blame God for that? We need to take responsibility. He entrusted us with the power of choice. If we misuse it and turn our back on Him, how is that His fault? By extension, if He gave us the opportunity to succeed, how does our failure become evidence for His absence?
However, if we come and seek Him in trust, it shows our love. What else can we offer the God that spoke the universe into being?