Ecclesiastes warns against going to the temple and making sacrifices but not having any understanding of God or of life. He wants people to accept the wisdom he's dishing out, not to just keep mindlessly performing rituals. He says God doesn't care about the things the fools are babbling.
He then warns against failing to fulfill the vows you make to God. He sees that it's better to never make a vow, than to keep failing to live up to the ones you do make. The Teacher's policy towards God is one of fear and cautious reverence. Ecclesiastes doesn't know what to make of the Big Man, but he's nervous about him.
Mo' Money, Mo' Vanity
The poor are still being oppressed. Ecclesiastes—or, Ol' Man Eckles, as we suddenly feel like calling him—says this shouldn't shock anybody. The world is like a pyramid, with people all trying to get on top of each other, working up to the next level—but there's always someone more ambitious and more arrogant higher up, ready to stomp a boot in your face.
Money doesn't lead to any enjoyment. If you got a lot of wealth and possessions, the only sure bet you have is just to enjoy seeing them sit there, says Eckles. It's vanity! Poor laborers at least get a satisfying night's sleep, but the rich have too much stuff to be able to slumber contentedly. They're either worrying about everything they have, which keeps them up, or they've gorged themselves on too many high-quality foods, and their indigestion is giving them insomnia.
Money, says Eckles, can vanish as soon as you get it. Or you might get piles of treasure and never be able to enjoy them, or lose them in a bad investment. Just as you came into the world without anything, you'll go out of the world without anything: naked. (He's giving a shout-out to Job 1:21, here.)
Here, he returns back to the point he repeated earlier: eat, drink, be merry, and try to enjoy your work. (He likes to really hammer these things home.) Eckles says God will make sure that some people are able to deal with life, by keeping them fixed on these simple joys.