v1-8: The cycle, or pendulum, of life. These things are not so much right or wrong, but are the cycle of life, the ordinary experience of ordinary people. But without God this is meaningless; with God these is an enjoyment of all of life.
Some things are outside human control, whilst other things are by man's decision; and material things have their place.
For Christ, there was a time to be born (Gal 4.4) and a time to die (Rom 5.6).
There is an order here (v3-4); kill then heal, tear down then build, weep then laugh, mourn then dance; repentance leads to restoration, sorrow to fruitfulness.
v9-11: Eternity in our hearts, the image of God in each one, the eternal soul; even without true faith, there ought to be some knowledge of God.
For the believer, there is the burden of the tension between this life and the next; the transitory nature of this life versus the etermal promise of the next life. Eternity in our hearts is waiting for and straining for its new home.
v12-13: Apart from God, a man only has the work of his hands to enjoy. There is some enjoyment in it, but there is so much more that he is missing.
v14-15: God's works are manifest, so that men should fear Him. The theme of the fear of God recurs here; 5.7; 7.18; 8-12-13; and 12.13, where it is the conclusion of the whole matter. We are all accountable to God, but we must beware of fatalism, that prevents us from working.
v16-17: Injustice may prevail now, but God will bring judgment upon all.
v18-22: Man's ignorance and impotence in the face of death. Man and animals die (compare 2.14-16, where wise and foolish men die). If life is to have any meaning, there must be something more than what we see. The writer accepts this, and points to a hereafter (Prov 23.18); the man of faith has such vision, and he is motivated by God.