The two composers were only a year apart in age, and both of them had the distinction of maturing as a composer while still in their teen years. Mendelssohn especially matured early on, as two of his most popular compositions, the String Octet and Overture To A Midsummer Night's Dream were both written by the time he was seventeen. They both admired J.S.Bach's music as Chopin played Bach extensively and used the preludes and fugues of The Well Tempered Clavier to keep his fingers limber before recitals. Mendelssohn was a key figure in the revival of Bach's music as he arranged and conducted the St. Matthew Passion in 1829. The two had a certain classisism as part of their artistic makeup, although it took a different course in each other's work.
There was a composer that also had an influence on both Chopin and Mendelssohn, Carl Maria von Weber. Specifically, it was Weber's Konzertstück For Piano that served as a model for Mendelssohn's works for piano and orchestra. This can be seen in the structure of Mendelssohn's Capriccio Brilliant For Piano and Orchestra. Mendelssohn's work begins with an introduction played andante, that is similar in structure and feeling to the beginning of Weber's Konzertstück. From the introduction the music segues into the music at a faster tempo and more dramatic in nature, the beginning of the first theme. This first theme is expanded upon with a few different motifs thrown in for good measure until there is a slight slowing of the tempo which signals the opening of the second theme which is first played by the orchestra. This second theme has a resemblance to the march section of Weber's work. The development section follows, and the recapitulation begins with the first theme followed by the second theme which is transformed to the minor mode and ends the work.
In 1845 Chopin told Mendelssohn in a letter:
“Let me remind you that even if you do possess friends and admirers worthier and closer to you, none is more sincere than I.”Sadly, both composers also shared an early death. Mendelssohn in 1847 of a stroke when he was 38 years old, Chopin in 1849 of tuberculosis when he was 39 years old. While Chopin's music never really went out of fashion, Mendelssohn's did. Mendelssohn was never a part of the 'New Music' movement of Wagner and Liszt and that Nazi Germany banned his music because of his Jewish heritage didn't do his reputation any good. There has been a revival and reevaluation of Mendelssohn and he is now regarded as a great Romantic Era composers.