While the Idea of freedom can be derived directly from the moral law as a postulate thereof, the proof of the reality of the two other Ideas is effected indirectly by means of the concept of the “highest good,” in which reason conceives a union of perfect virtue and perfect happiness.  The moral law requires absolute correspondence between the disposition and the commands of reason, or holiness of will.  But besides this supreme good (bonum supremum) of completed morality, the highest good (bonum consummatum) further contains a degree of happiness corresponding to the degree of virtue.  Everyone agrees in the judgment that, by rights, things should go well with the virtuous and ill with the wicked, though this must not imply any deduction from the principle previously announced that the least impulse of self-interest causes the maxim to forfeit its worth:  the motive of the will must never be happiness, but always the being worthy of happiness.  The first element in the highest good yields the argument for immortality, and the second the argument for the existence of God. (1) Perfect correspondence between the will and the law never occurs in this life, because the sensibility never allows us to attain a permanently good disposition, armed against every temptation; our will can never be holy, but at best virtuous, and our lawful disposition never escape the consciousness of a constant tendency to transgression, or at least of impurity.  Since, nevertheless, the demands of the (Christian) moral law continue in their unrelenting stringency to be the standard, we are justified in the hope of an unlimited continuation of our existence, in order that by constant progress in goodness we may draw nearer in infinitum to the ideal of holiness. (2) The establishment of a rational proportion between happiness and virtue is also not to be expected until the future life, for too often on earth it is the evil man who prospers, while the good man suffers.  A justly proportioned distribution of rewards and punishment can only be expected from an infinite power, wisdom, and goodness, which rules the moral world even as it has created the natural world.  Deity alone is able to bring the physical and moral realms into harmony, and to establish the due relation between well-being and right action.  This, the moral argument, is the only possible proof for the existence of God.  Theology is not possible as speculative, but only as moral theology.  The certitude of faith, moreover, is only different from, not less than, the certainty of knowledge, in so far as it brings with it not an objective, but a subjective, although universally valid, necessity.  Hence it is better to speak of belief in God as a need of the reason than as a duty; while a logical error, not a moral one, should be charged against the atheist.  The atheist is blind to the intimate connection which exists between the highest good and the Ideas of the reason; he does not see that God, freedom, and immortality are the indispensable conditions of the realization of this ideal.