Charles Ellicott Commentary Ecclesiastes 3:12

"I know that there is nothing better for them, than to rejoice, and to do good so long as they live." — Ecclesiastes 3:12 (ASV)

I know.—Literally, I knew: i.e., I came to know. The writer is relating the conclusions at which he successively arrived.

To do good.—This phrase is always used elsewhere in a moral sense: “to act rightly.” When enjoyment is meant, the phrase used is, as in the next verse, “to see good;” but the context seems to require that this sense should be given to the phrase in this verse also.