The Sermon is based on Matthew 13:31-3:
He put another parable before them, saying, “The kingdom of heaven is like a grain of mustard seed that a man took and sowed in his field. It is the smallest of all seeds, but when it has grown it is larger than all the garden plants and becomes a tree, so that the birds of the air come and make nests in its branches.”
He told them another parable. “The kingdom of heaven is like leaven that a woman took and hid in three measures of flour, till it was all leavened.”
You may find the audio link here if you wish to suffer through it. Also note that there is an option to download it there (using the button which says “download” underneath the link which says “listen”).
This sermon is a model of clarity. I really loved the letter from Martin Van Buren on railroads, too funny.