Mendelsohn composed the 3rd organ sonata in 1844, but he no longer played it publicly at concerts because he died in 1847. The sonata is based on the chorale "Aus tiefer Not schrei ich zu dir". The fact that the opening part is sometimes played at weddings is due to Mendelsohn himself, because he played this part at the wedding of his sister Fanny Hensel.
The added Andante is one of the loveliest pieces Mendelsohn composed for organ - in my opinion.
The Seifert organ in Goch is very well suited for early romantic works such as those by Mendelsohn.