The worldview in Ecclesiastes is clearly different from what we find later in the New Testament in a few different ways. Throughout the book, the Teacher's refrain comes through: 'All is vanity and a chasing after wind.' His application of the refrain produces some results that may puzzle or even offend those who strive to be faithful disciples of Jesus.
In my vain life I have seen everything; there are righteous people who perish in their righteousness, and there are wicked people who prolong their life in their evildoing. Do not be too righteous, and do not act too wise; why should you destroy yourself? - Ecclesiastes 7:15-16
The Teacher has observed what happens to righteous people. They get treated like they're wicked. They're frowned upon. Others don't like them. They get taken advantage of. His solution: don't be too righteous. Preserve yourself. Meanwhile, Jesus says, 'Those who save their life will lose it, but those who lose their life for my sake will find it.' Jesus had a different take on righteousness: be righteous. You'll actually save your life by doing it.
A sidebar: Yes, this is 'the Bible Jesus read,' to borrow a phrase. But while we see Jesus operate within his tradition in many ways, we also see him operate outside it. Consider his statements about the sabbath. There may even be other instances in the Hebrew Bible where prophets and others disagree with what the Teacher of Ecclesiastes has to say. Consider the strong critiques of those too comfortable to consider the righteousness that God sets forth for them.
The other piece of the Teacher's worldview that is clearly different from what we get in the New Testament and 'orthodox' Christianity is his concept of the afterlife. He mentions heaven four times. In all of them, he presents heaven as a place apart from earth and apart from human beings. This is where God lives, a place 'above' human beings. In the meantime, we all end up in Sheol:
Enjoy life with the wife whom you love, all the days of your vain life that are given you under the sun, because that is your portion in life and in your toil at which you toil under the sun. Whatever your hand finds to do, do with your might; for there is no work or thought or knowledge or wisdom in Sheol, to which you are going. - Ecclesiastes 9:9-10
Sheol is the Israelite concept of the place of the dead, perhaps not unlike Hades in Greek mythology. Everyone goes there. Good works, loving God, acceptingJesusChristasyourpersonalLordandSavior...none of these things 'get' you into heaven or 'get' you out of hell (the latter of which is foreign to the Old Testament). There is Sheol, to which everyone goes.
So one aspect of Ecclesiastes that has been fascinating is that the Teacher's worldview clashes so much with 'traditional' concepts of Christian belief. It illustrates so clearly and beautifully the diversity of thought in the Christian Bible, and presents a strong case against claims of inerrancy.
Don't get me wrong. That's not primarily why I would read it. This was just one observation made while moving through this lesser-known work. The Teacher shares his thoughts on accepting and enjoying one's lot in life and making the most of one's time on earth. He cautions against being too consumed with gathering wealth or wisdom, stating that since we all die, we shouldn't obsess over such things. One of my favorite quotes comes toward the very end:
Of anything beyond these, my child, beware. Of making many books there is no end, and much study is a weariness of the flesh. The end of the matter; all has been heard. Fear God, and keep his commandments; for that is the whole duty of everyone. - Ecclesiastes 12:12-13
He cautions against having your nose crammed in books all the time. You're not accomplishing anything besides making yourself tired. Go eat and drink. Go get some sun. Go serve God. What I like the best is that for the Teacher, studying and serving God are not necessarily the same thing. Maybe there are moments when they intersect (how to know God's commandments without studying them?), but there's more to it.
But then again, 'don't be too righteous.' Yeah, whatever.