432Hz is a fundamental frequency of nature which means that its harmonics and overtones resonate in concert with the universe. When the open A string on the guitar is tuned to A=432Hz instead of the current standard of 440Hz, this is called Verdi's A. Classical musicians such as Verdi and Mozart used A=432Hz tuning because the music is said to be softer and brighter, giving greater clarity and is easier on the ears. Ancient instruments from Egypt, Greece and other cultures used a scale where A=432Hz. Even the Stradivarius violin is tuned to A=432Hz, so what has changed?
There is a theory that the change from 432Hz to 440Hz was dictated by Nazi propaganda but it had actually already been decided in 1885 and The American Federation of Musicians accepted A=440Hz tuning as the standard pitch in 1917. Around 1940 the United States introduced 440 Hz worldwide.
There is a growing movement to switch back to A=432Hz but this is no small task as it would require new instruments. Most woodwind instruments cannot play in 432Hz because changing the pitch will also change the internal harmonic structure of the whole instrument.