This paper addresses two questions concerning the attribution of mystery to God. First, if Christianity is neither rationalistic nor agnostic concerning the knowledge of God, then what is the proper understanding of mystery when it is attributed to God? Second, if mystery conditions all theological thinking, how can the proper understanding of mystery be applied systematically across the full range of theological reflection? The response to the first question has three parts. First, God is incomprehensible not because we do not have access to God. God communicates God's self and we can know God's essence but we cannot comprehend God. Second, Thomas Aquinas shows us how we can know God yet God remains incomprehensible. Third, I elucidate the analogy of proper proportionality in arguing that although we do not fully know what we are talking about when we speak of God our concepts are not meaningless. In responding to the second question, I argue, in response to Karl Rahner's use of mystery in his treatment of the problem of suffering, that God's power cannot be absolute but must be related to God's goodness if one is to preserve the mystery of God across the full range of theological reflection.