1 sn Mustard seeds are known for their tiny size.
2 tn Mark 4:31-32 is fairly awkward in Greek. Literally the sentence reads as follows: “As a mustard seed, which when sown in the earth, being the smallest of all the seeds in the earth, and when it is sown, it grows up…” The structure has been rendered in more idiomatic English, although some of the awkward structure has been retained for rhetorical effect.
3 tn Grk “the birds of the sky” or “the birds of the heaven”; the Greek word οὐρανός (ouranos) may be translated either “sky” or “heaven,” depending on the context. The idiomatic expression “birds of the sky” refers to wild birds as opposed to domesticated fowl (cf. BDAG 809 s.v. πετεινόν).
4 sn The point of the parable seems to be that while the kingdom of God may appear to have insignificant and unnoticeable beginnings (i.e., in the ministry of Jesus), it will someday (i.e., at the second advent) be great and quite expansive. The kingdom, however, is not to be equated with the church, but rather the church is an expression of the kingdom. Also, there is important OT background in the image of the mustard seed that grew and became a tree: Ezek 17:22-24 pictures the reemergence of the Davidic house where people can find calm and shelter. Like the mustard seed, it would start out small but grow to significant size.