8 All things are full of labour; man cannot utter it: the eye is not satisfied with seeing, nor the ear filled with hearing.
[AD 397] Ambrose of Milan on Ecclesiastes 1:8
Therefore incline to him of whom the psalmist says, “He has not taken his soul in vain.” To speak now of the troubles of this life, the person has taken his soul in vain who is constructing the things of the world and building the things of the body. We arise each day to eat and drink; yet no one is filled so that he does not hunger and thirst after a short time. Daily we seek profit, and to greed there is set no limit. “The eye will not be satisfied with seeing, nor the ear with hearing.” He that loves silver will not be satisfied with silver. There is no limit to toil, and there is no profit in abundance. We desire each day to know what is new, and what is knowledge itself but our daily sorrow and abasement?

[AD 420] Jerome on Ecclesiastes 1:8
"All
things are full of toil, man cannot utter it: the eye is not satisfied with
seeing, nor is the ear filled with hearing.
"It is difficult
to know not just about physics but also about ethics. And discourse is not able to explain the
natural causes of things, nor to see those things that are hidden, (as the
scope of this work demands); nor, once you have begun to learn is it possible to
arrive at the greatest understanding by listening alone. For if we now look in the mirror in mystery
and in part know and in part prophesy, consequently discourse will not be able
to explain what it does not know; nor is the eye able to see where it is blind;
nor are the ears filled by what they do not hear. At the same time this must be noted, that all
words are wearying and are learnt with great difficulty, contrary to those who
idly make prayers that an acquaintance with the Scriptures will come to them.

[AD 600] Olympiodorus of Alexandria on Ecclesiastes 1:8
All writings, both of secular and of divine wisdom, yield instruction when effort is applied.