“How do the Kingdom parables (Matthew 13) relate to the epistles from Christ to the Churches?”
Parable: The Tares and the Wheat
A sower plants a bunch of wheat, but an enemy (Satan) comes along and plants tares, which are an annoying weed. The angels can’t sort it out until the end.
In other words, there is sin in the world, and there are people who do Satan’s work of making life really rough for the believers. The Persecuted Church had it really rough