The Parable of the Sower - The Key to All Parables.

And he said unto them, Know ye not this parable? and how then will ye know all parables?   4:13

It is said that Jesus taught 46 parables in the Gospels. Being as how this was one of the chief methods of communication by the Man Who spake as no man ever spake and taught with authority like no other, It is best for us to know the basics of the parable.

I thank "gotquestions.org" for the following insight for parables:

A parable is, literally, something "cast alongside" something else. Jesus' parables were sorties that were "cast alongside" a truth in order to illustrate that truth. His parables were teaching aids and can be thought of as extended analogies or inspired comparisons. A common description of a parable is that it is an earthly story with a heavenly meaning. 

We find, in verse 2, this parable being introduced as Jesus teaching them "in His doctrine." Which simply meant that the parable was His conveyance of His instruction. 

So, in brief, what key does this parable offer for the unlocking of all of the 45 other parables?

Mainly the following:

God sows the seed of the Word of God into the field, which is the world (more specifically, the heart of the individual). That ground is either receptive to the seed, or is not conducive to its germination, growth and fruitfulness.

I feel that the field (heart) referred to is the individual heart of every individual to whom the seed is introduced, including believers.

Therefore, it is incumbent upon me, individually, to be receptive to God's Word however it is conveyed to me; whether by my reading, hearing or meditation. If I prepare my heart to be receptive to the seed of the Word, it will find good ground and will reproduce in me abundantly.

This prepares my heart to receive the teachings of all of my Lord's parables and teachings.