What was the overall and final conclusion of Solomon?
There has been some discussion among scholars about who wrote Ecclesiastes, whether it was Solomon or someone else. I submit that it was authored by The Holy Spirit so it does not really matter who wrote it.
It is written by The Holy Spirit in Ecclesiastes chapter 1:
1 The Words of the Preacher, the son of David, king in Jerusalem.
2 “Vanity of vanities,” says the Preacher. “Vanity of vanities! All [that is done without God’s guidance] is vanity [futile, meaningless—a wisp of smoke, a vapor that vanishes, merely chasing the wind].”
The writer expands on futility in chapter 2:
9 So I became great and excelled more than all who preceded me in Jerusalem. My Wisdom also remained with me.
10 Whatever my eyes looked at with desire I did not refuse them. I did not withhold from my heart any pleasure, for my heart was pleased because of all my labor; and this was my reward for all my labor.
11 Then I considered all which my hands had done and labored to do, and behold, all was vanity and chasing after the wind and there was no profit (nothing of lasting value) under the sun.
Each of us has a choice to focus on things of temporary value or things of lasting, Eternal value.
Chapter 3:
11 HE has made everything beautiful and appropriate in its time. He has also planted Eternity [a sense of Divine purpose] in the human heart [a mysterious longing which nothing under the sun can satisfy, except God]—yet man cannot find out (comprehend, grasp) what God has done (His overall plan) from the beginning to the end.
12 I know that there is nothing better for them than to rejoice and to do good as long as they live;
13 and also that every man should eat and drink and see and enjoy the good of all his labor—it is the gift of God.
14 I know that whatever God does, it endures forever; nothing can be added to it nor can anything be taken from it, for God does it so that men will fear and worship Him [with awe-filled reverence, knowing that He is God].
Walking in the Fear of THE LORD it vital for us to understand our Divine purpose. All is summed up in the final chapter:
Chapter 12:
11 The Words of the wise are like [prodding] goads, and these collected sayings are [firmly fixed in the mind] like well-driven nails; they are given by one Shepherd.
12 But beyond this my son, [about going further than the Words given by one Shepherd], be warned: the writing of many books is endless [so do not believe everything you read], and excessive study and devotion to books is wearying to the body.
13 When all has been heard, the end of the matter is: fear God [worship Him with awe-filled reverence, knowing that He is Almighty God] and keep His commandments, for this applies to every person.
14 For God will bring every act to judgment, every hidden and secret thing, whether it is good or evil.
Wisdom commands us to walk in The Fear of THE ALMIGHTY GOD!