...if you wish to get pure air into your room, or if you go for a walk in the fresh air, think of the pure and of the unclean heart. Many of us like to have pure air in the room (and this is an excellent habit), or are fond of walking in the fresh air, but they do not even think of the necessity of the purity of the spirit or heart (of, so to say, spiritual air, the breath of life); and, living in the fresh air, they allow themselves to indulge in impure thoughts, impure movements of the heart, and even impurity of language, and most impure carnal actions.

...if you wish to get pure air into your room, or if you go for a walk in the fresh air, think of the pure and of the unclean heart. Many of us like to have pure air in the room (and this is an excellent habit), or are fond of walking in the fresh air, but they do not even think of the necessity of the purity of the spirit or heart (of, so to say, spiritual air, the breath of life); and, living in the fresh air, they allow themselves to indulge in impure thoughts, impure movements of the heart, and even impurity of language, and most impure carnal actions.