Mustard seed

The mustard plant Jesus speaks of is almost certainly Brassica nigra, the black mustard, an annual that grows wild and is also cultivated for its sharp, oily seeds. The seeds are tiny — roughly a millimetre across, in the same family of order of magnitude as a poppy seed — and in Jewish proverbs of the time were the standard image for "the smallest measurable thing." Yet by midsummer the plants tower three to four metres on the shores of the Sea of Galilee, with branches sturdy enough that finches and warblers do indeed land on them. Jesus uses this contrast twice. In Matthew 13 the mustard seed is the kingdom of heaven: a thing planted small and almost overlooked, growing into a refuge where the birds of the air come and nest — an echo of the great kingdom-tree of Daniel 4 and Ezekiel 17, here scaled down to garden size. In Matthew 17 the same seed becomes the yardstick of faith: faith the size of a single grain is enough to tell a mountain to move. The shock is not the smallness, but how much smallness can do when it is real.