The Mustard Grain. Much is said about the mustard seed, but most of the time people don't know about the mustard plant.
Mustard in Greek is sinomai, and means flamed, a plant of the tetradynamia siliquosa class, distinguished by its yellow cruciform flowers, with expanding chalice, and its smooth, square pods close to the stem. Its seed was probably the smallest known to the Jews; And although its normal height does not exceed four feet, yet a species grows to three to five cubits, with a tapered, striped stem and spreading branches.
And so we have what Christ said
Mat 13:31 Another parable proposed to them, saying, The kingdom of heaven is like a mustard seed, which a man took and planted in his field;
Mat 13:32 which is, in fact, the smallest of all seeds, and, when grown, is larger than vegetables, and becomes a tree, so that the birds of the sky come to nest in its branches.
See how small a mustard seed is, but when it becomes a plant it spreads into a tangle like a mountain. Here it is defining that the majesty of the kingdom is developing and growing. So is the concept of the kingdom of heaven. The rationale is that something small develops things that are not destructive. So is the word of God. Faith is also idealized as something for the good, for something eternal.
So everything that is for eternity is similar to the kingdom of Heaven.