Simplify the following text for a Grade 10 native English-speaking person.
Original: He did not often conduct opera , but he did conduct at the Royal Opera House : in 1936 with Gustave Charpentier 's opera Louise in 1936 and in 1954 the first performance of Walton 's Troilus and Cressida .
Simplified: In 1936 , he conducted his first opera at Covent Garden , Gustave Charpentier 's Louise . He did not return to the Royal Opera House to conduct opera again until 1954 , with Walton 's Troilus and Cressida , although he did conduct the incidental music for a dramatisation of The Pilgrim 's Progress given at the Royal Opera House in 1948 .