Simplify the following text for a Grade 12 native English-speaking person.
Original: Stoics were concerned with the active relationship between cosmic determinism and human freedom , and the belief that it is virtuous to maintain a will ( called prohairesis ) that is in accord with nature .
Simplified: It concerns the active relationship between cosmic determinism and human freedom , and the belief that it is virtuous to maintain a will ( called prohairesis ) that is in accord with nature .