Plowing hard hearts

In the parable of the sower (Matt. 13 or Luke 8), the seed that fell on the good ground produced a great crop, while seeds that fell on other kinds of ground did not. I heard Joyce Myers the other day talking about all these agricultural metaphors and I heard plowing and realized that good ground is plowed ground. Plowed ground is soft ground and unplowed is hard. Seeds need soft ground for a variety of reasons.

In Matthew 13, when Jesus explains the parable of the sower, He also quotes Isaiah 6, explaining why he teaches in parables and in the Isaiah passage, hardness of heart as a phrase is used to describe people who are unable to receive teaching or be fruitful.

So my question is, how do we get our hearts plowed so that we are receptive to the Word and become fruitful? Do we do it or does God or do life's circumstances that come our way? Why are some people hard hearted while others are soft? Why are some people receptive and others are not?