Full Idea
The existence must be postulated of a cause of the whole of nature, itself distinct from nature, which contains the ground of the exact coincidence of happiness with morality.
Gist of Idea
We have to postulate something outside nature which makes happiness coincide with morality
Source
Immanuel Kant (Critique of Practical Reason [1788], I.II.II.V)
Book Reference
Kant,Immanuel: 'Critique of Practical Reason (Third edition)', ed/tr. Beck,Lewis White [Library of Liberal Arts 1993], p.131
A Reaction
I can see that we need a concept of how happiness could be made proportional to morality, but I can't make sense of the assumption that it is actually possible, and hence something must exist that would achieve it.