The text of Ecclesiastes 3:11 is enigmatic, not just because the sentence itself is ambiguous but also because English translations render the Hebrew words quite freely as if they translate the different words.
KJV: He hath made every thing beautiful in his time: also he hath set the world in their heart, so that no man can find out the work that God maketh from the beginning to the end.
ASB: He hath made everything beautiful in its time: also he hath set eternity in their heart, yet so that man cannot find out the work that God hath done from the beginning even to the end.
JPS: He brings everything to pass precisely at its time; He also puts eternity in their mind, but without man ever guessing, from first to last, all the things that God brings to pass.
NRSV: He has made everything suitable for its time; moreover he has put a sense of past and future into their minds, yet they cannot find out what God has done from the beginning to the end.
GWV: It is beautiful how God has done everything at the right time. He has put a sense of eternity in people’s minds. Yet, mortals still can’t grasp what God is doing from the beginning to the end ⸤of time⸥.
NAB: God has made everything appropriate to its time, but has put the timeless into their hearts so they cannot find out, from beginning to end, the work which God has done.
As you see, Qohelet says God put/set something in the human mind, and that “something” is either “the world” or “the eternity.” Alternatively, “a sense of past and future,” “a sense of eternity,” or “the timeless” can replace “eternity.”
Regardless of the sentence’s meaning, what exactly is the word used in the Hebrew text here? It is עלם(olam), meaning “long time,” “duration,” “future time,” etc. The word is often translated as “eternity,” though its actual meaning does not precisely correspond to the modern concept of eternity.
So it is bizarre to render עלם(olam) into “the world.” Some translations, including KJV that have “the world” for the term עלם(olam), mislead the reader. Though it is difficult to choose a word for עלם(olam), “the world” is certainly not the best choice; “eternity” is not the perfect choice but much better a choice than “the world.”
What does Qohelet mean by that, though? To understand, we need to comprehend the context.
I think the first part of the sentence(11a), “He brings everything to pass precisely at its time (JPS),” should be separated from the rest of the sentence (11b) because v. 11a better reads with the previous verses. That is, in 3:1-8, Qohelet talks about things that happen in our lives, such as the time of killing, dying, laughing, crying, throwing, embracing, etc.
Then, he complains that the things we do “weigh down” (GWV, v. 10) us, but it is what God gives us to be afflicted with. So he asks a rhetorical question, ” What gain have the workers from their toil?” meaning “nothing. He thinks everything happens in God’s appointed time, which is supposed to be appropriate or right.
But what Qohelet experiences or observes tells something else; it is not always appropriate. Rather, God has given us only toils that afflict us, not benefit us. Then how could he say that “he [God] has made everything suitable for its time?” (NRSV v. 11a) Qohelet seems to admit that everything that God has given us to be afflicted with occurs precisely at its time, but he doesn’t seem to admit that everything is beautiful.
Therefore, it is awkward to take Qohelet’s words, “he has made everything beautiful in its time,” literally. At best, Qohelet only mechanically confesses his religious conviction here without empathy, or it is his sarcasm about his complaint.
Then, he goes on to state another complaint in v 11b: God put “עלם(olam)“ in our minds, and yet we do not understand how God controls everything from the beginning to the end. In other words, God made us understand a complex concept–“long duration of time” like “from the beginning to the end” (a sense of eternity)–but God does not allow us to apprehend how God manages to control what happens (such as time of killing and dying, loving and hating, thrwoing and embracing, etc) in that long duration of time at all.
Qohelet is a difficult text in many ways. Its Hebrew text is difficult to translate, and the content itself is also confusing and contradictory in many places. Chapter 3 is an example.
In 3:1-8 Qohelet lists things that happen in our lives, and in v. 11a, Qohelet, unlike what I explained, indeed empathized that everything is beautiful. Or the complete opposite understanding is true as I explained above. I think the context, both immediate and larger, suggests the latter.