Evil exists, not because GOD ordained all evil acts as a necessary part of creation, but because GOD, by His own authority, gave man two gifts. The first is the gift of free will, the second gift is the ability to use the first. GOD gave man free will HE withholds His power to prevent the wrong and evil choices that HE foreknows will occur as a result of man freely and recklessly implying these gifts.
Reward and punishment is impossible if man were good or evil through necessity and not choice. Man was by GOD constituted free, master of his own will and power which allowed man to know GOD. The goodness of GOD having provided man for the pursuit of the knowledge of GOD.