This agreement, moreover, may be explained on the ground that the comments and interpretations in question are very old, and were included both in the Babylonian Talmud and in the Palestinian sources used by the redactor of Shir haShirim Rabbah.
Jellinek thinks[9] that there were several aggadic midrashim to Song of Songs, each of which interpreted the book differently, one referring it to the exodus from Egypt, another to the revelations on Mount Sinai, and a third to the Tabernacle or the Temple in Jerusalem; and that all these midrashim were then combined into one work, which (with various additions) forms the present Shir ha-Shirim Rabbah.
According to Jellinek, this midrash is older than the Pesikta de-Rav Kahana, which (he holds) has borrowed entire passages from it.
The author of Shir ha-Shirim Rabbah, intending to compile a running midrash on Song of Songs, took the comments on the several verses from the sources which he had at hand, and the changes and transpositions which he made are similar to those made by the redactor of the Yalkut Shimoni; in fact the midrash is similar in many ways to a "yalkut".
The material borrowed from these sources constitutes a large part of the midrash, and it throws a light also on the redactor's method.