The parable’s focus on the seeds is an allegory for those who hear the word of the kingdom proclaimed. The parables describe the varying receptiveness to what they hear; all hear the same word. Yet each type of person is identified as what was sown in a certain place. This might strike us as odd since we are biased to understand the “seed” as the Word of God proclaimed, but understanding of the parable rests on the interaction of the unvarying seed with the various types of ground.
seed sown on the path… without understanding – To understand is more than an intellectual grasp of the message; cf. the contrast in 7:24ff. between hearing and ‘doing’ the word. The word which is only heard is easy prey for the evil one. It is a non-starter.
seed sown on rocky ground… receives it with joy – But to start is not necessarily to finish. Here the word is received (not ‘understood’) with joy, but joy without understanding and commitment cannot last: lasts only for a time is literally ‘is temporary’. Tribulation is a general term for suffering which comes from outside; persecution is deliberately inflicted, and usually implies a religious motive. Falls away is literally ‘is tripped up’ (cf. 5:29–30); it is not a gradual loss of interest, but a collapse under pressure.
seed sown among thorns… This time the soil is good, but it is already taken up. The world (as opposed to the kingdom of God) offers both anxiety and lures (the normal meaning of this word, apatē, is ‘deceit’), each occupying the attention and energy in a way that prevents even good soil from bearing fruit.
seed sown on rich soil – Hearing is matched with understanding, and the consequences are a superabundant yield.
In the context of Jesus’ ministry, the parable serves to explain why it is that the good news of the kingdom meets with such a varied response from enthusiastic acceptance to outright rejection.
The fault lies not in the message, but in those who receive it. People are both inadequate in themselves to respond as the word of the kingdom requires (compacted and shallow soil), and also exposed to competing pressures from outside (tribulation and persecution, anxieties and lures, and behind them all the evil one himself). The wonder is not that some do not produce fruit, but that any do.
But here lies the parable’s encouragement both to Jesus’ followers then and to all who since then have preached this same gospel; not all will respond, but there will be some who do, and the harvest will be rich.
If you wonder if you are part of the harvest… take a look at your feet. Don’t like what you see? Find rich soil and plant yourself there.