Mustard Seed Sumeru means that a tiny mustard seed can contain a huge Mount Sumeru. It is a metaphor for the fact that all the forms are not real, and that the huge and small can be compatible.

Mustard seed: mustard seed; Sumeru: the great mountain in ancient Indian legend. It is a Buddhist saying that the tiny mustard seed can contain the huge Mount Sumeru. Metaphorically speaking, there is also greatness in smallness. In fact, Sumeru, mustard seed is a metaphor, mainly to develop our wisdom, to recognize the "self-centeredness".