I've started preaching through Ecclesiastes and expect to preach on it at least through Easter, maybe a few weeks more. You can check out the commentaries and books I'm using on the left sidebar part way down. Some are more helpful than others and I'm not "clicking" with any of them totally. At least not yet.
Who wrote Ecclesiastes? Ecclesiastes says it's "Qohelet" or the "assembler" probably pointing to 1 Kings 8 where Solomon gathers God's people at the Temple dedication. It's a "Son of David" and a "King in Jerusalem" according to 1:1. A lot of evidence points to Solomon, and most of the conservative, pastoral writers say it's Solomon.
Many of the commentators say someone else borrowing the voice of Solomon. I don't think we must say it's Solomonic since the writer of Ecclesiastes doesn't make that explicit claim, but I haven't read anyone who denies the fact that we are intended to have Solomon in mind. And I wonder if Solomon would purposefully keep his name off the writing (though not his identity) because of how he lived his life as an idolater (1 Kings 11).
We need to keep our "solas" in place here and only demand what Scripture claims, but I don't see any problem with believing the writer is Solomon. Sure there are internal reasons to wonder, like shifting from a "framers" perspective (Eccl 1:1-11, 12:8-14) to Qohelet's perspective. But why must this mean dual authorship or the framing of someone else's writings? As Peter Leithart writes on his blog about commentators who rejects Solomonic authorship: "The imagination of the commentator has not come near to reckoning with the imagination of the speaker." In other words, it could very well be Solomon creatively writing for impact. Why must we assume other authors/framers?
Solomon speaks much of life "under the sun." To me it clearly points us to Genesis 3 where God is explaining what life is going to be like after the fall. With Adam we hear there is going to be toil (hard work, even misery) and sweat. Under the sun + toil = sweat. Nice imagery in the linking of these writings.
I think Ecclesiastes is about the best efforts of the best man with every privilege to make sense out of life under the sun (after the fall). And last Sunday I told my people that the only hope we have "under the sun" is to know the One "beyond the sun."