Background: Olivier Eugene Charles Prosper Messiaen (French: [olivje mesja]; December 10, 1908 - April 27, 1992) was a French composer, organist, and ornithologist, one of the major composers of the 20th century. His music is rhythmically complex; harmonically and melodically he employs a system he called modes of limited transposition, which he abstracted from the systems of material generated by his early compositions and improvisations. He wrote music for chamber ensembles and orchestra, vocal music, as well as for solo organ and piano, and also experimented with the use of novel electronic instruments developed in Europe during his lifetime. He travelled widely and wrote works inspired by diverse influences ranging from Japanese music, the landscape of Bryce Canyon in Utah and the life of St. Francis of Assisi.
Context: Shortly after his release from Gorlitz in May 1941, Messiaen was appointed a professor of harmony at the Paris Conservatoire, where he taught until his retirement in 1978. He compiled his Technique de mon langage musical ("Technique of my musical language") published in 1944, in which he quotes many examples from his music, particularly the Quartet. Although only in his mid-thirties, his students described him as an outstanding teacher. Among his early students were the composers Pierre Boulez and Karel Goeyvaerts. Other pupils included Karlheinz Stockhausen in 1952, Alexander Goehr in 1956-57, Tristan Murail in 1967-72 and George Benjamin during the late 1970s. The Greek composer Iannis Xenakis was referred to him in 1951; Messiaen urged Xenakis to take advantage of his background in mathematics and architecture in his music.  In 1943, Messiaen wrote Visions de l'Amen ("Visions of the Amen") for two pianos for Yvonne Loriod and himself to perform. Shortly thereafter he composed the enormous solo piano cycle Vingt regards sur l'enfant-Jesus ("Twenty gazes upon the child Jesus") for her. Again for Loriod, he wrote Trois petites liturgies de la presence divine ("Three small liturgies of the Divine Presence") for female chorus and orchestra, which includes a difficult solo piano part.  Two years after Visions de l'Amen, Messiaen composed the song cycle Harawi, the first of three works inspired by the legend of Tristan and Isolde. The second of these works about human (as opposed to divine) love was the result of a commission from Serge Koussevitzky. Messiaen stated that the commission did not specify the length of the work or the size of the orchestra. This was the ten-movement Turangalila-Symphonie. It is not a conventional symphony, but rather an extended meditation on the joy of human union and love. It does not contain the sexual guilt inherent in Richard Wagner's Tristan und Isolde because Messiaen believed that sexual love is a divine gift. The third piece inspired by the Tristan myth was Cinq rechants for twelve unaccompanied singers, described by Messiaen as influenced by the alba of the troubadours. Messiaen visited the United States in 1949, where his music was conducted by Koussevitsky and Leopold Stokowski. His Turangalila-Symphonie was first performed in the US in 1949, conducted by Leonard Bernstein.  Messiaen taught an analysis class at the Paris Conservatoire. In 1947 he taught (and performed with Loriod) for two weeks in Budapest. In 1949 he taught at Tanglewood. Beginning in summer 1949 he taught in the new music summer school classes at Darmstadt. While he did not employ the twelve-tone technique, after three years teaching analysis of twelve-tone scores, including works by Arnold Schoenberg, he experimented with ways of making scales of other elements (including duration, articulation and dynamics) analogous to the chromatic pitch scale. The results of these innovations was the "Mode de valeurs et d'intensites" for piano (from the Quatre etudes de rythme) which has been misleadingly described as the first work of "total serialism". It had a large influence on the earliest European serial composers, including Pierre Boulez and Karlheinz Stockhausen. During this period he also experimented with musique concrete, music for recorded sounds.
Question: What was the song about?

Answer:
The second of these works about human (as opposed to divine) love was the result of a commission from Serge Koussevitzky.