Matthew Poole and continuators on Job 21:21

21. For what pleasure hath he in his House after him , when the number of his Months is cut off in the midst ?

Or, For what desire, or care, or study hath he for, or concerning (as Beth is oft used) his House, i. e. his Children. When he is dead and gone he cares not what becomes of his Children, as Irreligion commonly makes men unnatural, he is not concerned nor affected with their Felicity or misery. See Ch. 14. 21. And therefore God doth punish both him and his Children whilest he lives, v. 19, 20. Or thus: What delights can he take in the thoughts of the Glory and Happiness of his Posterity, when he finds that he is dying a violent and untimely Death? So this is a farther proof that this man is neither happy in himself, nor with reference to his Posterity.

When that number of Months which by his Constitution, and the course of Nature, he might have lived, is diminished and cut off by the hand of Violence.