Kohelet Rabbah 2:1 קהלת רבה ב׳:א׳

“I said in my heart: Come now, I will experiment in joy, and see goodness; and, behold, it too is vanity” (Ecclesiastes 2:1).
“I said in my heart: Come now, I will experiment in joy” – Rabbi Pinḥas and Rabbi Ḥizkiyya in the name of Rabbi Simon bar Zavdi: Rabbi Pinḥas said: “I will experiment [anasekha]” and I will experiment;¹The midrash is interpreting the word anasekha to mean anaseh ko, I will experiment with this, and when experimenting one generally investigates different options (Matnot Kehuna). I will try matters of Torah and I will try matters of heresy. I will flee [anusa] from matters of heresy to matters of Torah, “and see goodness,” the goodness of Torah. “And, behold, it too is vanity” – the verse should have said only: “And behold, it too is joy,”²As the verse states “I will experiment in joy.” and you say: “And, behold, it too is vanity”? Rabbi Ḥizkiyya said in the name of Rabbi Simon bar Zavdi: All the Torah that you study in this world is vanity relative to the Torah in the World to Come, as in this world, a person studies Torah and forgets. But, regarding the World to Come, what is written there? “I placed My Torah in their midst” (Jeremiah 31:32).
And the Rabbis say: The evil inclination will melt before the good inclination.³They interpret the word anasekha to mean “will melt” [yinatekh] (Matnot Kehuna). “And see goodness” – the goodness of the World to Come. Rabbi Yona in the name of Rabbi Simon bar Zevid: Any serenity that a person sees in this world is vanity relative to the serenity of the World to Come, as in this world, a person dies and bequeaths his serenity⁴His prosperity, which facilitates his serenity in this world. to another, but regarding the World to Come it is written: “They will not build and another inhabit” (Isaiah 65:22).