4:13 What does Jesus mean by what he says here?

To better understand what Jesus means here we need to study the context in which He said it (cp Mk 4:1-9).

This is called the parable of the sower.

It concerns the nature and development of the kingdom of heaven in its present earthly aspect.

Jesus gave this parable as a type of all the rest of His parables.

His questions to the disciples in V13 implies that if one can understand this parable one can understand all the others, for in this parable are the principles of interpretation in all of them (cp Mk 4:14-20).