Mark 4:30-34 Herein, we bring to a close this block of teaching material – specifically, Jesus teaching in parables “beside the sea” (Mark 4:1) – with the parable of the mustard seed (Mark 4:30-32). The kingdom of God is like what happens to the smallest of all seeds (v. 30-31). You’ll note that there is no description of the growth process. What we have here is a study in comparison/contrast: the beginning from the end. When the mustard seed grows up it “becomes larger than all the garden plants” (v. 32, ESV). Full grown, it is a source of provision and protection (for “the birds of the air”).
If we read this parable in light of the present manifestation of the kingdom of God – the person of Jesus – what we find does not appear to be particularly significant: an itinerant Rabbi from Nazareth, 
the son of a Carpenter. Oppressive Rome is still in power! In fact, at this point in the narrative, Jesus’ ministry has not ventured much outside of the northern shores of Galilee. But remember the mustard seed! The day will come when the kingdom of God surpasses the glory of all the kingdoms of the earth. Jesus is Lord (kurios), not Caesar! William Lane says: “The mustard seed is the word of God proclaimed by Christ. This word possesses the power which one day will make all things new.” (NICNT, p. 172)*
If this is true, what great power we (His present day disciples) yield in our “hands” as His ambassadors (2 Cor. 5:20), as we continue the mission of Jesus (which was carried on by the original 12 disciples, and continues today) – proclaiming the good news of the kingdom of God!
Mark concludes this section with the statement that He “spoke the word to them, as they were able to hear it” (Mark 4:33) – i.e., in parables. Jesus teaches the crowds about the kingdom of God (in general). But to His disciples He explains the mystery of the Kingdom as present in His person! Truly a veiled message destined to be revealed!
Until next time, my friends… Follow Jesus!
*In the interest of full disclosure, I am deeply indebted to Lane’s interpretation throughout this post