Other ways to say  the third line, undivided, shows that, while there is no state of peace that is not liable to be disturbed, and no departure (of evil men) so that they shall not return, yet when one is firm and correct, as he realises the distresses that may arise, he will commit no error. there is no occasion for sadness at the certainty (of such recurring changes) ; and in this mood the happiness (of the present) may be (long) enjoyed.