Tertullian, Against Marcion 2.13

The logic runs like this: evil erupted later, and only then did God's goodness begin to engage the adversary. That same justice of God also found another task — now directing goodness in opposition to the adversary — so that, once its freedom is set aside (the freedom by which God is good of his own accord, dispensing favor according to each person's merits: offering it to the worthy, denying it to the unworthy, withdrawing it from the ungrateful, and thereby exacting vengeance on all rivals), the whole work of justice becomes the management of goodness. What it condemns by judging, what it punishes by condemning, what you call raging — all of it profits the good, not the evil. Finally, the fear of judgment drives toward the good, not the evil. For goodness did not suffice to commend itself; now it labors under the adversary. Even if it is commendable in itself, it is not also preservable, because it is now conquerable by the adversary — unless some power of fear were present to compel even the unwilling to seek and guard the good. With so many allurements of evil conquering the good, who would pursue what he could despise with impunity? Who would guard what he could lose without danger? The road of evil is broad and far more traveled: would not everyone stumble onto it if nothing were feared on it? We tremble at the Creator's terrible threats, and we are hardly torn away from evil. What if he threatened nothing? Would you call this justice evil because it does not favor evil? Would you deny this is good because it looks out for the good? What kind of god do you want? What kind would suit evildoers? Under whom would sins rejoice? At whom would the devil mock? Would you judge that god good who could make man more evil by the security of sin? Who is the author of good, if not also the exactor? Therefore who is a stranger to evil, if not also an enemy? Who is an enemy, if not also a conqueror? Who is a conqueror, if not also a punisher? Thus the whole God is good, so long as he is entirely for the good. Thus finally he is all-powerful, because he is powerful both to help and to harm. It is less to be only beneficial, because he can do nothing else but benefit. With what confidence could I hope for good from such a one, if he can only do that? How could I pursue the reward of innocence, if I do not also fear the punishment of guilt? I must distrust, lest the one who lacked the power for either part fail to reward either. So far justice is also the fullness of divinity itself, exhibiting God as perfect — both Father and Lord: Father by clemency, Lord by discipline; Father with gentle power, Lord with severity; Father to be loved piously, Lord to be feared necessarily — to be loved because he prefers mercy to sacrifice, and to be feared because he does not want sin; to be loved because he prefers the sinner's repentance to death, and to be feared because he does not want his sinners who are no longer repenting. Therefore the law defines both: you shall love God, and you shall fear God. He set one thing before the supplicant, another before the transgressor.