Evil exists in the world. But God is all-powerful. Why then doesn't He remove all evil from the world?
God gave Adam and Eve a choice in the garden they chose wrong which started the evil. They made the choice for us and now we have to finish the role they started by making that choice.
Evil is our nature and God wants us to have a relationship with him that is why Christ died on the cross to wipe the slate clean.
We will never not be sinners on this world and we have a choice to know and accept that but again it is Gods will that we choose where we stand.
I look at it kinda like we are all pawns in a game of chess between two powers it is in who's side you want to be on.
God does not get rid of the evil because the choice was already made for us and we must except that and he allowed the choice to be made and Man and woman chose wrong.
What would the world been like had they not taken the serpents offer of eating from the tree of knowledge of good and evil one can only imagine.