Expositor's Bible Commentary Commentary Mark 4:32

"yet when it is sown, groweth up, and becometh greater than all the herbs, and putteth out great branches; so that the birds of the heaven can lodge under the shadow thereof." — Mark 4:32 (ASV)

This is the third and last of the parables about the seed sown. The mustard seed was proverbial for its smallness but when grown, it becomes a huge treelike shrub.

The main point of the parable is that the kingdom of God has insignificant and weak beginnings, but a day will come when it will be great and powerful. We should not judge the significance of the kingdom by the size of its beginning.