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.

What is central to morality is rational self-constraint (acting from duty), in cease where there is no other incentive to do your duty except that the moral law commands it.

Popular religion since the time of Kant and Fichte has gone in a direction they tried to prevent and that has been disastrous for the humanity both of believers and of the rest of us. Look at the role of religion in Republican presidential primaries if you need any confirmation of this last statement.

Those who employ their modest talents as best they can do make a contribution to a better human future.

It would be nice, wouldn't it? if we could get comfortable about the problem of freedom. Kant thinks that we can't.

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

Fichte is concerned with freedom as non-domination.