Мидраш к Диврей ха-ямим Б 2:1

... “And David went and he took the bones of Saul and the bones of Jonathan his son from the men of Jabesh- gilead… And he brought up from there the bones of Saul and the bones of Jonathan his son…” (Shmuel II 21:12-13) What did David do? He went and gathered all the elders and great ones of Israel, crossed the Jordan River, and came to Yavesh-gilead. He found the bones of Shaul and his son Yonatan, placed them in a casket and crossed back over the Jordan, as it says “And they buried the bones of Saul and Jonathan his son in the country of Benjamin in Zela, in the tomb of Kish his father and they did all that the king commanded…” (Shmuel II 21:14) What does ‘in Zela, in the tomb of Kish his father’ mean? It comes to teach us that they brought them to the border of Jerusalem and buried them there. Zela is next to Jerusalem, as it says “And Zelah, Eleph, and the Jebusite, which is Jerusalem…” (Yehoshua 18:28) ‘and they did all that the king commanded’ And what did the king command? He commanded that they carry Shaul’s casket from tribe to tribe. As Shaul’s casket entered each tribe’s territory all the men, women and children came out in order to perform an act of loving kindness to Shaul and his sons and thereby all of Israel would fulfill its obligation to loving kindness. This went on until they reached the land of his portion on the border of Jerusalem. Since the Holy One saw that they did loving kindness to Shaul and fulfilled the judgement of the Givonites He was immediately filled with mercy and sent rain upon the land, as it says “And God was entreated for the land after that.” (Shmuel II 21:14) From this we learn how close the Holy One brings those that are far away, even though they converted not for the sake of heaven. There is no need to even mention how he draws near righteous converts, “O Lord, all the kings of the earth will acknowledge You…” (Tehillim 138:4)

Another explanation: "And you shall take for yourselves on the first day" - in spite of all of that wisdom that is written about Shlomo (II Chronicles 2:1), "wisdom and knowledge are granted to you;" (I Kings 5:10-11) "And the wisdom of Shlomo grew... And Shlomo was wiser than all men," these four species were perplexing to him, as it is stated (Proverbs 30:18), "Three are there that are wondrous beyond me" - these three are the Pesach sacrifice, matsa and marror (bitter herbs) - "and four which I did not know" - these four are the four species of the lulav, that he sought to understand: "The fruit of a beautiful tree" - who will tell me that it is a citron (etrog)? All of the trees make beautiful fruit (and are hence called beautiful trees). "The branches of a date palm" - the Torah said, "take two palm branches (as 'branches' is in the plural) to praise with" and he only takes a [singular] lulav, which is the heart of the date palm. "And a branch of a braided tree (a myrtle)" - who will tell me that it is a myrtle? Behold, in another place it says (Nechemiah 8:15), "Go out to the mountain and bring olive branches, etc" (the verse continues to list several species and mentions myrtles alongside branches of a braided tree, seemingly indicating that they are two different species). "And brook willows" - all trees grow in the water! [Hence,] "and four which I did not know." He came back and mentioned them a different time, as it is stated (Proverbs 30:29), "There are three that are good, etc." - these are the four species, that each and every one in Israel goes and runs and takes from them for himself, to praise the Holy One, blessed be He. And [the four species] appear small in the eyes of man but they are great in front of the Holy One, blessed be He. And who explained to Israel that they were these four species, which are the citron, the palm branch, the myrtle, the willow? The Sages; as it is stated (Ibid., verse 24), "they are very wise sages."