A connection can be make to the theme of the resurrection: the seed
that drops into the soil "to die" is resurrected into a bigger and
more fruitful existence. This thought is certainly also present
in the 2 Corinthian "new creation" passage: "one has died for all;
therefore all have died. And he died for all, so that those who live might live no
longer for themselves, but for him who died and was raised for them."
(Verses 5:14-15)
With regard to the mustard seed, Crossan makes a good point about
its the interpretation:
[The point] is not just that the mustard plant starts as a
proverbially small seed and grows into a shrub of three or four feet,
or even higher, it is that it tends to take over where it is not
wanted, that it tends to get out of control, and that it tends to
attract birds within cultivated areas where they are not particularly
desired. And that, said Jesus, was what the Kingdom was like: not like
the mighty cedar of Lebanon and not quite like a common weed, like a
pungent shrub with dangerous takeover properties. Something you would
want in only small and carefully controlled doses. If you could
control it. [1]