Reference request for Functional Analysis Does anyone know a book that motivates the beginning of functional analysis in a clear way?
By "clear," I mean that it shows why one would want to define Hilbert spaces and why the theorems are motivated. I know of Dieudonne's History of Functional Analysis, but I am looking for something that also explains the theory. 
 A: In addition to books on history (J. Dieudonne, History of functional analysis (review) is very good and easy reading), I recommend some
books by the founding fathers:


*

*John von Neumann, Mathematische Grundlagen der quantum Mechanik, (there are English and Russian translations). Functional analysis (in Hilbert space) is related to quantum mechanics in the same way as Calculus to classical mechanics.

*F. Riesz and B. Szőkefalvi-Nagy, Functional analysis (multiple editions in French, German, Russian, English).

*P. Levy, Problèmes concrets d'analyse fonctionnelle. Avec un complément sur les fonctionnelles analytiques par F. Pellegrino. 2d ed. Gauthier-Villars, Paris, 1951. (There is a Russian translation).

*L. Schwartz, Mathematics for the physical sciences. Hermann, Paris; Addison-Wesley Publishing Co., Reading, Mass.-London-Don Mills, Ont. 1966.
A: Three articles that I found interesting:
Hellinger, E.; Toeplitz, O., Integralgleichungen und Gleichungen mit unendlichvielen Unbekannten, 184 S. Mit einem Vorwort von E. Hilb. Leipzig, B. G. Teubner (Encyklopädie der mathematischen Wissenschaften mit Einschluß ihrer Anwendungen, II C 13) (1927). ZBL53.0350.01.
Steen, L.A., Highlights in the history of spectral theory, Am. Math. Mon. 80, 359-381 (1973). ZBL0264.46001.
Narici, Lawrence; Beckenstein, Edward, The Hahn-Banach theorem: The life and times, Topology Appl. 77, No.2, 193-211 (1997). ZBL0919.46005.
