Music note: This is the part that the band The Byrds (mentioned in the "In a Nutshell") took their hit song from.
Ecclesiastes says that there's a season for everything, and he gives a list of seven pairs of opposing things, saying that each has its time. There's a "time to kill, a time to heal," and "a time to love, a time to hate." Every pair he gives is like this—a positive combined with a negative. There's a bit of a Yin-Yang vibe.
Then Ecclesiastes goes back to discussing work or toil. He says that God has given everything its proper time to occur, and put the idea of "Eternity" or "the world" into the minds of people. He means that God has put it into the heads of human beings that there's something so totally beyond them—a limitless future and a limitless past—that they just can't wrap their minds around it.
Time keeps spinning around, he says, and the same things keep happening. It's a little like Groundhog Day. But God is above it all.
Ecclesiastes complains that there's little justice in the world. Wicked people are in the places that good people should be occupying, and they act without justice, corrupting things that should be just.
Even though Ecclesiastes says he doesn't know if there's life after death—although he believes in God—he says that the good and the bad will, somehow, be rewarded or punished. He's not sure how this will happen, but he says it will.
Unlike other parts of the Bible, Ecclesiastes doesn't think humans are better than animals. He says that human beings and animals both die and turn back into the dust God made them from. He also says they're powered by the same breath, the same spirit.
Regarding this spirit, Ecclesiastes says he doesn't know if it ascends back to God after death, or if it just sort of dissolves. We guess he's not the ultimate authority on everything, then.
Again, he returns back to the theme of trying to enjoy the work you have while there's still time. He's not saying to be a work-a-holic—just to find something creative to do to fill up the time you have, which has already been set by God.