What is the meaning of Mark 4:30-34?

30 And he said, Whereunto shall we liken the kingdom of God? or with what comparison shall we compare it? 31 It is like a grain of mustard seed, which, when it is sown in the earth, is less than all the seeds that be in the earth: 32 But when it is sown, it groweth up, and becometh greater than all herbs, and shooteth out great branches; so that the fowls of the air may lodge under the shadow of it. 33 And with many such parables spake he the word unto them, as they were able to hear it. 34 But without a parable spake he not unto them: and when they were alone, he expounded all things to his disciples. (Mark 4:30-34 KJV)

William Burkitt’s Commentary

BURKITT : | Mr 4:1-2 | Mr 4:3-9 | Mr 4:10-13 | Mr 4:14-20 | Mr 4:21-25 | Mr 4:26-29 | Mr 4:30-34 | Mr 4v35-41 | KJV Comm

The design of our Saviour in this parable is to show how the gospel church, from small and little, from unlikely and contemptible beginnings, should spread and increase, fructify and grow up, like as mustard-seed, one of the smallest of grains, grows up to a considerable tallness; even so, Christ foretells that the gospel should spread and increase, nations and countries becoming Christians.

Hence learn, That how small beginnings so ever the gospel had in its first plantation, yet by the fructifying blessing of God it has had and shall have a wonderful increase.