In Matthew 13:31, the mustard seed represents the good we have before developing a spiritual orientation; it is the smallest of all the seeds, because we often think that we do good on our own. Anything we do on our own is evil through and through, but since we are engaged in the process of being reborn, we have a trace — the smallest possible trace — of goodness. (Arcana Coelestia 55[3, 4])

3568. 'And he said, Bring it to me, and I will eat from my son's venison' means a desire to join natural truth to itself by means of good. This is clear from the meaning of 'eating' as joining together and making one's own, dealt with in 2187, 2343, 3168, 3513 (end), and from the meaning of 'my son's venison' as truth acquired from good, dealt with in 3309, 3501, 3508. The fact that a desire is meant is self-evident.