David O’Connor gives a remarkably clear explanation of the difference between defense and theodicy, from the opening of God and Inscrutable Evil:
Could evil for which we can discern neither point nor justification ever exist in a God-made world? Even if it could, does not such evil make it improbable that the world was made by God? Why would a God-made world contain evils for which we can discover no point or justification? And, even if there is a reason that a world made by God contains evils of that sort, why so much and so many varieties?
…Of its nature, a defense tries to ensure that [theism] survives the charge or attack against which [it] is being defended. That being so, a successful defense does not have to prove theism true and atheism false. Nor does it have to establish that the evils cited in a given antitheistic argument are logically consistent with God, or that their occurrence is probable if God exists. Furthermore, it does not have to explain the existence of any or all evil in a supposedly God-made world. To do any of these things would constitute a substantive, and, in the first case, a maximal defense of theism, whereas a nonsubstantive and considerably more minimal defense, if successful, is sufficient. Thus, against a prosecuting argument whose aim is to show that certain facts of evil are inconsistent with God, a defense succeeds if it shows that the prosecuting argument fails to establish its conclusion. And likewise for a defense against an argument aiming to show that some fact or facts of evil are improbable on theism…
A defense, understood in any of the ways just specified, is an appropriate response to the first two of the four questions posed above, but not to the third or the fourth. To answer those questions would require a theodicy, a theodicy being an attempt to answer, in a systematic and comprehensive way, the question, “what is the source of the evil we find, and why does God permit it?” So understood, a theodicy tries to explain the ways of God to human beings, whereas a defense need not.
…While a theodicy’s task is wider than a defense’s, it is neither the more basic nor the more important… This is because… if the theistic defenses are not up to their job, then [theism] stares defeat in the face. And if theism is defeated, then the [theodicy] project will be redundant. But if the defenses hold, then while the need to solve the [problems of theodicy] remains, their solution could plausibly be understood as a work in progress and its completion not urgent, or, at least, less urgent than the need for a defense. In this sense, then, defense has priority over theodicy.
Please keep this in mind as you read my Arguing About Evil series.