Adam Clarke on Luke 12:21

So is he - That is, thus will it be. This is not an individual case; all who make this life their portion, and who are destitute of the peace and salvation of God, shall, sooner or later, be surprised in the same way.

Layeth up treasure for himself - This is the essential characteristic of a covetous man: he desires riches; he gets them; he lays them up, not for the necessary uses to which they might be devoted, but for himself; to please himself, and to gratify his avaricious soul. Such a person is commonly called a miser, i.e. literally, a wretched, miserable man.