Kant sketches out here what is to follow. Most of these two chapters focuses on comparing the situation of theoretical and of practical reason and therefore discusses how the Critique of Practical Reason compares to the Critique of Pure Reason.
The Critique of Pure Reason was a critique of the pretensions of pure theoretical reason to attain metaphysical truths beyond the ken of applied theoretical reason. Its conclusion was that pure theoretical reason must be restrained, because it produces confused arguments when applied outside its sphere. However, the Critique of Practical Reason is not a critique of pure practical reason, but rather a defense of it as being capable of grounding behavior superior to that grounded by desire-based practical reasoning. It is a critique, then, of applied practical reason's pretensions. Pure practical reason must be restrained but rather cultivated.
Kant tells us that while the first Critique presented God, freedom, and immortality as unknowable, the second Critique will mitigate that claim. Freedom is knowable because it is revealed through the force of the moral law. God and immortality are not, but now (practical) reason requires belief in them. One might still be dissatisfied, wanting, say, proof of God's existence. Kant here invites his dissatisfied opponent to actually provide such a proof, believing that none is forthcoming. The discussion of freedom Kant holds to be especially important, for empiricists insist on thinking of it as a purely psychological thing in the phenomenal world, a complete confusion according to Kant.
The Critique of Practical Reason can stand alone from the earlier Groundwork for a Metaphysics of Morals, although it addresses some criticisms leveled against that work. In particular, Kant will address the issue of why he did not first discuss the highest good and then define the moral law in terms of it. A complete classification of duties will not occur in the second Critique because such a classification depends on how people contingently are. This work will proceed on a higher level of abstraction.
While valid criticisms against the Groundwork of the Metaphysics of Morals are to be addressed, Kant excoriates those criticisms he does not find helpful. He suggests that some of the gaps reviewers find in his arguments are in fact only in their brains, which are too lazy to grasp his ethical system as a whole. As for those who charge him with writing incomprehensible jargon, he challenges them to find more suitable language for his ideas, or otherwise to prove that they really are meaningless. Fortunately, Kant reassures us, that while the speculations of the first Critique required language very unlike common speech, this will be less true in the second Critique.
Finally, the sketch of the second Critique is presented in the Introduction. It is modeled on the first Critique. First, the Analytic will investigate the operations of the faculty in question. Next, the Dialectic will investigate how it can go astray. Finally, the Doctrine of Method follows, which will only be loosely analogous to its corresponding first Critique section, discussing how to bring about psychological influence of pure practical reason.