Passing Through

[Ecc. 5:20] For he shall not much remember the days of his life; because God answereth him in the joy of his heart.
For he shall not - The person who acts in this way, extracts all the good requisite from life. He passes through things temporal so as not to lose those that are eternal: "Calm and serene, the road of life to him, or long or short, rugged or smooth, with thorns overspread, or gay with flowers, is but a road. Such fare as offers grateful he accepts, and smiling to his native home proceeds."
Summery of 18-20:
1. What it is that is here recommended to us, not to indulge the appetites of the flesh, or to take up with present pleasures or profits for our portion, but soberly and moderately to make use of what Providence has allotted for our comfortable passage through this world. We must not starve ourselves through covetousness, because we cannot afford ourselves food convenient, nor through eagerness in our worldly pursuits, nor through excessive care and grief, but eat and drink what is fit for us to keep our bodies in good plight for the serving of our souls in G-d's service. We must not kill ourselves with labour, and then leave others to enjoy the good of it, but take the comfort of that which our hands have labored for, and that not now and then, but all the days of our life which G-d gives us. Life is G-d's gift, and He has appointed us the number of the days of our life (Job 14:5); let us therefore spend those days in serving the L-rd our G-d with joyfulness and gladness of heart. We must not do the business of our calling as a drudgery, and make ourselves slaves to it, but we must rejoice in our labour, not grasp at more business than we can go through without perplexity and disquiet, but take a pleasure in the calling wherein G-d has put us, and go on in the business of it with cheerfulness.
2. What is urged to recommend it to us:
A. That it is good and comely to do this. It is well, and it looks well. Those that cheerfully use what G-d has given them thereby honour the giver, answer the intention of the gift, act rationally and generously, do good in the world, and make what they have turn to the best account, and this is both their credit and their comfort; it is good and comely; there is duty and decency in it.
B. That it is all the good we can have out of the things of this world: It is our portion, and in doing thus we take our portion, and make the best of bad. This is our part of our worldly possession. G-d must have His part, the poor theirs, and our families theirs, but this is ours; it is all that falls to our lot out of them.
3. That a heart to do thus is such a gift of G-d's grace as crowns all the gifts of His providence. If G-d has given a man riches and wealth, He completes the favour, and makes that a blessing indeed, if withal He gives him power to eat thereof, wisdom and grace to take the good of it and to do good with it. If this is G-d's gift, we must covet it earnestly as the best gift relating to our enjoyments in this world.
4. That this is the way to make our own lives easy and to relieve ourselves against the many toils and troubles which our lives on earth are incident to: He shall not much remember the days of his life, the days of his sorrow and sore travail, his working days, his weeping days. He shall either forget them or remember them as waters that pass away; he shall not much lay to heart his crosses, nor long retain the bitter relish of them, because G-d answers him in the joy of his heart, balances all the grievances of his labour with the joy of it and recompenses him for it by giving him to eat the labour of his hands. If he does not answer all his desires and expectations, in the letter of them, yet he answers them with that which is more than equivalent, in the joy of his heart. A cheerful spirit is a great blessing; it makes the yoke of our employments easy and the burden of our afflictions light.
Remember - So as to disquiet himself. He will not remember much, looking back with disappointment, as the ungodly do (2:11), on the days of his life.
The days - The troubles; days being put here for evil or, sad days.
Answereth – G-d answers his prayers in giving him "power" to enjoy his blessings. He desires, in giving him solid joy and comfort.