We commit not only theoretical error but also moral wrong in objectifying ourselves or other rational beings, ignoring their capacities for free action and communicative interaction with us.

Kant's aim was to develop a religion within the boundaries of mere reason (that is, reason unaided by special empirical revelation) and then to ask about existing ecclesiastical faith (especially about Christianity, and the Lutheran Christianity of his time and place) how this revealed faith must be interpreted if it is to be reconciled with reason, and even seen as a wider (though morally optional) extension of a religion of reason.

Fichte is concerned with freedom as non-domination.

Kant does not regard freedom as an item of faith because it is too basic to our agency to be related to any end.

It was an important part of Mendelssohn's philosophical and religious view that the traditional rationalist proofs for God's existence should be sound an convincing. Kant thought they were not. So Kant's critique was world-shaking for Mendelssohn.

As I understand it, Kantian constructivism is partly a position in normative ethics and partly a position in metaethics. In metaethics, it is the position that ethical claims have truth values, but their truth conditions consist not in a set of objective facts to which they correspond, but instead in the outcome of some procedure of deliberation resulting in decisions about what to do.

We can establish empirical criteria for free actions, and investigate human actions on the presupposition we are free.