This is a "Marmite" moment, a product which is advertised as something you either love or hate. In my view it is the same with the Rachmaninov Vespers, you will either love or hate them, personally I love them. They are considered to be one of Rachmaninov's finest musical achievements and one of the greatest musical achievements of the Russian Orthodox Church.
The Vespers are a very challenging acapella choral composition by Sergei Rachmaninov which were written and premiered in 1915. The work is better known as the Vespers but infact the texts have been taken from the Russian Orthodox All-Night Vigil ceremony. The Vigil was a traditional service celebrated before major feasts. As well as receiving high praise, they were infact one of Rachmaninov's favourite compositions, the other being his symphonic poem The Bells. So much so that he wanted the 5th movement of the Vespers to be sung at his funeral.
They were composed in less than two weeks in January and February 1915 and are particularly notable because Rachmaninov had stopped going to church. Their first performance was given in March 1915 partly to benefit Russian war effort. Nikolay Danilin conducted the all-male Moscow synodal choir. It was so warmly received that it was performed five more times within a month. However the Russian Revolution of 1917 and the rise of the Soviet Union led to a government condemnation of religious music in July 1918 and as such the Vigil remained unrecorded until 1965 though some 30 recordings have since been made.
I went to Russia a few years ago and I find it a fascinating country both in past and present and I also worked with a Russian monk choir whilst at EMI. For me this music is very 'Russian' sounding and encapsulates everything about the country, they sound old and established yet passionate, emotional and beautiful which is all achieved through a kaleidoscope of musical colours. They are very difficult to sing and make huge demands on intonation and breath control. Because the Russians tend to form their words in a different part of the mouth to many other western languages, to get the right sound I think you have to be Russian to sing these. There are many who undoubtedly disagree with me and indeed there is a new recording out by the Kansas City Chorale and I have no doubt it is very good. But the recording I am going to recommend is by the Latvian Radio Choir, it is breathtakingly beautiful, described in Gramophone Magazine as "a sublimely beautiful yet rapturous recording". Do give them a go.