Miriam T. Griffin (ed.), Seneca on Society: A Guide to De Beneficiis
(6.) 21. 1 'sciam', inquit, 'solem ac lunam nobis velle prodesse, si nolle potuerint; illis autem non licet non moveri' ('I might accept', he says, 'that the sun and the moon wish to do us a service, if they were able not to wish it; but they are not permitted not to be in motion'). The two objections—that they do not wish to help, and that they do not choose to perform the movement that conserves the universe—are answered in 21. 2–4 and 22–23. 2 respectively.
(6.) 21. 2 non ideo minus vult qui non potest nolle; immo maximum argumentum est firmae voluntatis ne mutari quidem posse (a person is not less willing because he cannot be unwilling; in fact, it is the greatest proof of a fixed intention, that it cannot be changed). The Stoic habit of comparing the gods to a vir bonus (good man) stems from their similar rational nature: they differ only in length of life (Prov. 1. 5). Seneca explains the fixed intention of the heavenly bodies in terms of the good man, whose character dictates his intention. This does not remove his moral responsibility: in fact, as he says at 21. 4, it explains it, since we are more to be praised or blamed for acts in character than for capricious ones. This kind of necessity is internal, not external, compulsion (see L–S, pp. 392–4).