Simplify the following text for a Grade 8 native English-speaking person.
Original: In his first subscription week he led the world premiere of John Adams ' On the Transmigration of Souls commissioned in memory of those who died on September 11 , 2001 .
Simplified: In his first subscription week he conducted the first ever performance of John Adams ' On the Transmigration of Souls . This work had been composed in memory of those who lost their lives on September 11 , 2001 .