What Should We Expect During The Church Age?
offers valuable insights, gleaned from the parables of Matthew 13. Contrary to the popular view, these parables describe the Church Age—not a mystical kingdom already among us that will grow until it overtakes the world. They do not teach that the world is getting better and will eventually usher in the kingdom through human effort. Instead, they paint a realistic and consistent picture of this present age. All 8 parables agree with each other and the full teaching of Scripture—unlike the common interpretation. For more detail, see
book The Coming Kingdom.
Context:
Right before these parables, Jesus’ offer of a literal kingdom to Israel is rejected by the nation's leaders (Matt. 12:24). Because they attribute His miracles to Satan, the kingdom offer is postponed, not canceled. Messiah then begins to speak in parables, revealing what characteristics believers should expect during this interim period—the Church Age. These characteristics are also called the "mysteries of the kingdom of heaven" (Matt. 13:11.)
The first 4 parables are taught to the crowds outside the house, by the Sea of Galilee.
The last 4 parables are taught privately to the disciples, inside the house.
Here is a summary of the first four parables:
Parable Name: Parable of the Sower
Reference: Matt. 13:1-9, 18-23
Main Point: The Gospel will be preached throughout this age with varying responses. Those who respond favorably (ie those who believe) will be provided additional revelation.
Parable Name: Parable of the Wheat & Tares
Reference: Matt. 13:24-30, 36-43)
Main Point: The saved and the unsaved will be mixed together and it will be difficult to distinguish between the two. The separation will not be made until the Second Coming.
Note: The separation of the saved and unsaved will not be made until the Second Coming.
Parable Name: Parable of the Mustard Seed
Reference: Matt. 13:31-32
Main Point: Christendom will grow significantly compared to the small beginnings of the First Century. However, the final form of Christendom will deviate from its biblically pure origins.
Note: A mustard seed produces an herb. But in the parable, the herb somehow becomes a tree 
This is not normal! Herbs do not transition to trees. Though the church started off as something pure, over the course of this age it becomes a deformed monstrosity that looks nothing like its humble beginnings.
Parable Name: Parable of the Leaven
Reference: Matt. 13:33
Main Point: Christendom will experience an increasing amount of doctrinal and moral corruption as the age progresses.
Note: In all other passages, both in the OT and the NT, leaven is used to represent something evil or pernicious. It makes sense that it also symbolizes something wicked or sinful in this passage. In contradistinction to the popular, kingdom now interpretation, the leaven does not mean the spreading of the gospel. Leaven is never used to symbolize something good in Scripture, ever. Even the Messiah used leaven to symbolize something evil (Matt. 16:11)
“The popular view is contradicted by the plain facts of history and by present-day experience… The Gospel has now been preached for nineteen centuries, yet not a single nation or state, no, not even a city, town or village, has been completely evangelized - let alone won to Christ! If the popular view is the correct one, then the Gospel is a colossal and tragic failure.”
(Pg, 121, The Coming Kingdom)