Jamieson, Fausset and Brown on Ecclesiastes 3:9

9. But these earthly pursuits, while lawful in their season, are "unprofitable" when made by man, what God never intended them to be, the chief good. Solomon had tried to create an artificial forced joy, at times when he ought rather to have been serious; the result, therefore, of his labor to be happy, out of God's order, was disappointment. "A time to plant" (Ec 3:2) refers to his planting (Ec 2:5); "laugh" (Ec 3:4), to Ec 2:1, 2; "his mirth," "laughter"; "build up," "gather stones" (Ec 3:3, 5), to his "building" (Ec 2:4); "embrace," "love," to his "princess" (see on Ec 2:8); "get" (perhaps also "gather," Ec 3:5, 6), to his "gathering" (Ec 2:8). All these were of "no profit," because not in God's time and order of bestowing happiness.