52 The verb זָכַר (zakhar, “to remember”) may be nuanced “to call to mind; to think about,” that is, “to reflect upon” (e.g., Isa 47:7; Lam 1:9; Job 21:6; 36:24; 40:32; Eccl 11:8); cf. 270 זָכַר 5; I זכר 2.
53 The word “fleeting” does not appear in the Hebrew text, but is supplied in the translation for clarity.
54 The term מַעֲנֵה (ma’aneh, Hiphil participle from II עָנָה, ’anah, “to be occupied”) refers to activity that keeps a person physically busy and mentally preoccupied, e.g., Eccl 1:13; 3:10; 5:19 ( ; 775 עָנָה II). The related noun עִנְיַן (’inyan,“business; occupation; task”) refers to activity that keeps man busy and occupies his time, e.g., Eccl 1:13; 2:26; 3:10 ( ; 775 עִנְיָן). The participle form is used to emphasize durative, uninterrupted, continual action.
55 Heb “with the joy of his heart.” The words “he derives from his activity” do not appear in the Hebrew, but they are added to clarify the Teacher’s point in light of what he says right before this.

In other versions

For he will not much remember the days of his life because God keeps him occupied with joy in his heart.

They seldom reflect on the days of their life, because God keeps them occupied with gladness of heart.

for he does not often consider the days of his life because God keeps him occupied with the joy of his heart.

God keeps such people so busy enjoying life that they take no time to brood over the past.

For he does not remember the brief days of his life, for God keeps his heart preoccupied with enjoyment of life.

For he shall not much remember the days of his life; because God answereth him in the joy of his heart.

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