Simplify the following text for a Grade 7 native English-speaking person.
Original: In 1979 , Sogyal Rinpoche chose the name Rigpaâ '' the innermost , essential nature of mindâ '' for his work .
Simplified: In 1979 , Sogyal Rinpoche chose the name Rigpa for his work . It means `` the innermost , essential nature of mind '' .