The rabbinic midrash on Exodus 15:13 was: «You have been gracious to us, for we had no good works to show» (cited in AJCT 40). (religion-online.org)
One last piece of background material to this parable is the saying in Midrash Lamentations Rabbah 4.2: «None of them (men of Jerusalem) would attend a banquet unless he was invited twice.» (religion-online.org)
The use of the term place to describe God is based on a rabbinic midrash from the third century (Genesis Raba, chapter 61). (religion-online.org)