Mt 13:31f “The kingdom of heaven is like a mustard seed that a man took and sowed in his field.  It is the smallest of all the seeds, but when it has grown it is the greatest garden plant and becomes a tree, so that the wild birds come and nest in its branches.”

Mk 4:30-32  “To what can we compare the kingdom of God, or what parable can we use to present it?  It is like a mustard seed that when sown in the ground, even though it is the smallest of all the seeds in the ground—when it is sown, it grows up, becomes the greatest of all garden plants, and grows large branches so that the wild birds can nest in its shade.” 

Jesus may have been standing near to a garden, where the cultivated, or black mustard might have been planted. Furthermore, Jesus is making a contrast between the size of the seed (which is very small) and the size of the resulting plant (which is a shrub some 3 feet high with branches capable of bearing the weight of small birds). The kingdom of heaven is like that: it started off with just Jesus and his disciples, but grew into a worldwide movement that would bear the hopes and fears of Gentiles as well as Jews and would last for thousands of years. (Adapted from HSB)

Some have been bothered about the accuracy of this statement (cf. also Mt 13:32). The mustard seed is a very small seed, but it is not as small as, say, a poppy seed. How then could Jesus say that it is ‘the smallest seed you plant in the ground’? This is a trivial problem, and can be easily resolved in one of two ways:

(a) A literal reading of the text should note that Jesus refers to the mustard seed as ‘the smallest seed you plant in the ground’; that is, it is the smallest seed that is commonly planted.  Harold Lindsell (The Battle for the Bible, p169) remarks:

‘From the Greek it is not clear that Jesus was saying that the mustard seed is the smallest of all the seeds on the earth.  He was saying that it is less than all the seeds…If Jesus was talking about the seeds commonly known to the people of that day, the effect of His words was different from what they would have been if He was speaking of all seeds on the earth.’

Here’s another attempt to pin our Lord’s words down to a level of precision that was probably not intended:

‘Jesus was talking to a group of people living in an agricultural society. His listeners were farmers. He didn’t say the mustard seed was the smallest seed on earth. He said the mustard seed “is the smallest seed you plant in the ground”. He is referring directly to the seeds they were using in their day to plant their gardens: “it grows and becomes the largest of all garden plants…”’ (J. Warner Wallace)

(b) It was not Jesus’ purpose (or the Evangelists’) to teach botany, but to make a point about the kingdom of God.   The mustard seed was proverbially small, and that is as much as we really need to know.  In any case, we have no reason to suppose that they knew anything other than the ‘scientific’ knowledge of their own day.

As Grant Osborne points out,

‘when Jesus said the mustard seed was “the smallest seed” (Mk 4:31), he was not making a scientific statement but using a hyperbolic contrast (smallest-greatest); the mustard seed was the smallest seed that produced such a large plant (v. 32). The same was true when Jesus talked of a camel going through a needle’s eye (Mk 10:25). This was the largest animal in Palestine through the smallest hole, to stress the incredible difficulty of converting the wealthy.’ (The Hermeneutical Spiral, p127)

Conclusion

I am not committed, a priori, to the doctrine of inerrancy.  I am therefore comfortable with the second view, (b).

There are more pressing matters for inerrantists and their critics to discuss.