Some inspiring quotes:
"Architecture is the only art in which the great struggle between the will of the spirit and the necessity of nature issues into real peace, in which the soul in its upward striving and nature in its gravity are held in balance (…)"
Georg Simmel, "The Ruin", Chapter I, 1911
"Architecture means building art [Baukunst], uniting two concepts in its name: the expertise, the mastery of the practical, useful discipline, and the art of abstract beauty (...) We have gone through times when they stood almost for opposite meanings. We have this time behind us"
Peter Behrens, 1901
"To look upon architecture only from one angle, such as the rational-constructive or the purely artistic, is a simplification and impoverishment"
Theo van Doesburg, "Die neue Architectur und ihre Folgen", 1925
"Not only the technological and not only the aesthetic, not only reason and not only sentiment, but the harmonic synthesis of both should be the architectural aim(...)"
J.P. Oud, "Holländische Architektur", 1926
"Life is what matters in all the fullness of its spiritual and concrete relations"
Mies van der Rohe, from a letter to Walter Riezler, 1926
"Architecture is the art above all others which achieves a state of Platonic grandeur, mathematical order, speculation, the perception of the harmony which lies in emotional relationships. This is the aim of architecture"
Le Corbusier, "Vers une Architecture", 1926
"The building art can only be unlocked from a spiritual center and can only be comprehended as a living process"
Mies van der Rohe, "The preconditions of architectural work", Lecture, 1926
"Fulfill the Law to gain Freedom"
Mies van der Rohe (around 1950)