Why Use Parables?
First, we must understand that parables were not given as a blessing, but as a judgment. They are not children's fare, but only for those willing to do the hard work of study.
“Why do You speak to them in parables?” He answered and said to them, “Because it has been given to you to know the mysteries of the kingdom of heaven, but to them it has not been given... Therefore I speak to them in parables, because seeing they do not see, and hearing they do not hear, nor do they understand.
In Matthew 12, the leaders of Israel (to whom the Lord was sent) exposed their disdain for his message of the kingdom. The Lord condemns their rejection of his wisdom:
The queen of the South will rise up in the judgment with this generation and condemn it, for she came from the ends of the earth to hear the wisdom of Solomon; and indeed a greater than Solomon is here.
The Lord and his disciples had been preaching the gospel of the kingdom (Matt 4:23; 9:35). This gospel was for ISRAEL ALONE (Matt 10). Note, the Lord revealed nothing about his death and resurrection until Matthew 16:21 (and they wouldn't believe him).
So, the parables of Matthew must be considered in this context. The Lord's ministry here is to Israel and the kingdom he speaks of reflects the "gospel of the kingdom" to Israel and Judah.
The Gospel of the Kingdom
We see the gospel of the kingdom of the kingdom being preached in that coming day "as a witness to all the nations" (v.14). The time frame, "and then the end will come."
"Then" should be understood as "at that time." This is very helpful as we read Matthew.
Looking back at John for a second, in the Lord's prayer for his disciples, he speaks plainly (not in difficult parables).
See, now You are speaking plainly, and using no figure of speech! (Greek: paroimía; Strong, "specifically an enigmatical or fictitious illustration: - parable, proverb").
Parables are used to (a) hide things from those who have closed ears and (b) reveal things to those who do the work of seeking with a pure heart. Parables have a surface meaning and application and a deeper, often prophetic, message.
Final thought: We no more preach the "gospel of the kingdom" from Matthew than we preach the "everlasting gospel" of Rev 14. In this age, we speak plainly of the "sacred secret gospel" of Ephesians. As we look at the parables in Matthew we need to grasp this concept. Without the context, we can be deceived. I've noticed that most false schisms and cults make a great deal of the parables. A coincidence? I think not.