This is no different than the Holy Trinity, a concept which is incomprehensible to human reason, yet firmly established as the foundation of Christian monotheism.
Free will establishes us as moral and rational beings, responsible for our own actions and decisions, not driven by necessity. It establishes sin as our rejection of God and ultimately rejection of God's will. Thus, sin is our 'creation,' not God's. Free will explains our fall from grace and points to god's love in our redemption.
Human restoration to grace can only be accomplished by the same mechanism by which man fell from grace: either he fell by free disobedience or he was predestined by cruel God to fall. Likewise, either we are passively "restored" by capricious God, or we are given a chance to come to Him in free obedience. Thus, just as the fall was born out of freedom, our coming to God must be free and not compelled.
good summary, imho.