The instruction of children should aim gradually to combine knowing and doing. Among all sciences mathematics seems to be the only one of a kind to satisfy this aim most completely.
The sum total of all possible knowledge of God is not possible for a human being, not even through a true revelation. But it is one of the worthiest inquiries to see how far our reason can go in the knowledge of God.
Human freedom is realised in the adoption of humanity as an end in itself, for the one thing that no-one can be compelled to do by another is to adopt a particular end. - 'Metaphysical Principles of Virtue
Philosophical knowledge is the knowledge gained by reason from concepts ; mathematical knowledge is the knowledge gained by reason from the construction of concepts.
...as soon as we examine suicide from the standpoint of religion we immediately see it in its true light. We have been placed in this world under certain conditions and for specific purposes. But a suicide opposes the purpose of his creator; he arrives in the other world as one who has deserted his post; he must be looked upon as a rebel against God. God is our owner; we are his property; his providence works for our good.
Natural science physics contains in itself synthetical judgments a priori, as principles. ... Space then is a necessary representation a priori, which serves for the foundation of all external intuitions.