Ecclesiastes is Koheles in Hebrew, may be questionable in its context first hand. But, its essence is undoubtedly critical to the whole of the Holy Bible. Ecclesiastes by King Solomon, teaches the true purpose of life based on his own experience.

A wake-up call to you who live to work; instead of work to live.

“All Is Futile”

The words of Koheles son of David king in Jerusalem: Futility of futilities — said Koheles — futility of futilities! All is futile!
1:1-2
A generation goes and a generation comes, but the earth endures forever.
:4
All the rivers flow into the sea, yet the sea is not full; to the place where the rivers flow, there they flow once more.
:7
All words are wearying, one becomes speechless; the eye is never sated with seeing, nor the ear filled with hearing.
:8
… There is nothing new beneath the sun.
:9
Sometimes there is something of which one says: “Look, this is new!” — it has already existed in the ages before us.
:10
I, Koheles, was king over Israel in Jerusalem.
:12
For with much wisdom comes much grief, and he who increases knowledge increases pain.
:18

1 The words of Koheleth son of David, king in Jerusalem.
2 Vanity of vanities, said Koheleth; vanity of vanities, all is vanity.
3 What profit has man in all his toil that he toils under the sun?
4 A generation goes and a generation comes, but the earth endures forever.
5 The sun rises and the sun sets, and to its place it yearns and rises there.
6 It goes to the south and goes around to the north; the will goes around and around, and the will returns to its circuits.
7 All the rivers flow into the sea, yet the sea is not full; to the place where the rivers flow, there they repeatedly go.
8 All things are wearisome; no one can utter it; the eye shall not be sated from seeing, nor shall the ear be filled from hearing.
9 What has been is what will be, and what has been done is what will be done, and there is nothing new under the sun.
10 There is a thing of which [someone] will say, “See this, it is new.” It has already been for ages which were before us.
11 [But] there is no remembrance of former [generations], neither will the later ones that will be have any remembrance among those that will be afterwards.
12 I am Koheleth; I was king over Israel in Jerusalem.
13 And I applied my heart to inquire and to search with wisdom all that was done under the heaven. It is a sore task that God has given to the sons of men with which to occupy themselves.
14 I saw all the deeds that were done under the sun, and behold, everything is vanity and frustration.
15 What is crooked will not be able to be straightened, and what is missing will not be able to be counted.
16 I spoke to myself, saying, “I acquired and increased great wisdom, more than all who were before me over Jerusalem”; and my heart saw much wisdom and knowledge.
17 And I applied my heart to know wisdom and to know madness and folly; I know that this too is a frustration.
18 For in much wisdom is much vexation, and he who increases knowledge, increases pain.