God wanted humans to worship him freely, not to act automatically. The existence of free will necessarily requires the possibility of evil choices. God does not will evil; he simply creates humans who make evil choices.

Objections:
Although this is often presented as a powerful argument, it is open to several objections.

• If freedom is good in itself, and therefore necessary in a perfect world, it is not necessarily implied that choices must involve good and evil. One can choose freely between good alternatives without becoming a mere robot. In any case, this argument simply ignores the original question. We asked not what the purpose of evil is in the world, but from whence it comes?
• Why does God require worship at all? If he is perfect, he should not need anyone to praise or adore him, certainly not flawed, deluded beings such as humans whose adoration can hardly be as rewarding as that of angels, who understand God much more fully and clearly.
• If the freedom to choose to do evil is essential to determine who should be saved, will the saved in Heaven also be free to commit sins? If not, is their state to be judged inferior to our own? Clearly not. So why not skip the mortal phase of existence with all its suffering and sin altogether and proceed directly from creation to heaven?
• If God knows all, he clearly knew before creating human beings that they would fall into sin. How can he be held innocent for sins which he knowingly made inevitable? Since we are told in the gospels that the majority of people go to Hell, God must knowingly have set up a system which is at least remarkably inefficient, if not actually wicked.