Avi Solomon has informed me that Samuel Johnson explicated Epictetus' Handbook 21 very well in The Rambler No. 17. Tuesday, May 15, 1750:
"A frequent and attentive prospect of that moment, which must put a period to all our schemes, and deprive us of all our acquisitions, is indeed of the utmost efficacy to the just and rational regulation our lives; nor would ever any thing wicked, or often any thing absurd, be undertaken or prosecuted by him who should begin every day with a serious reflection that he is born to die."
The Rambler, sections 1-54 (1750)