What is the moral lesson in the parable of the seed sower?

There is no moral lesson in the parable of the sower.

An explanation of the parable is given in Matthew 13:12-23, Luke 8:11-15 and Mark 4:14-20.

This parable is about the preaching of the Word - the planting of the seed of the gospel and the bearing of fruit in the hearts of people.

A parable is an illustration in order to explain a truth, to make the truth easier to understand. A parable puts something familiar alongside something unfamiliar to help people to understand spiritual truth by using everyday objects and relationships.

A parable is similar to a fable or an allegory or a proverb but parables are generally concerned with spiritual matters.