As is often the case, passages that one side find supportive another side views as providing strong refutation.
The Kingdom Parables
The parables of the kingdom are believed by postmillennialists to constitute a substantive piece of that doctrine's biblical basis. Postmillennialists hold that these parables teach of a church that starts small and gradually grows to encompass the earth, although even at the end some evil will be present. Other viewpoints, especially dispensationalism, have an entirely different perspective.
The Parable of the Sower
But the one who received the seed that fell on good soil is the man who hears the word and understands it. He produces a crop, yielding a hundred, sixty or thirty times what was sown." (Matt 13:23)
According to Pentecost, this passage indicates not an increase in the success of the gospel, but a decrease, contradicting postmillennialism and supporting dispensationalism:
During the course of the age, there will be a decreasing response to the sowing of the seed, from a 'hundredfold' to 'sixty' to 'thirty'. Such is the course of the age.202
[Editorial comment: I am not supposed to rebut the criticism but I can’t resist. The passage talks about multiplicative increases, so even the weakest one (thirty-fold) is quite impressive. And as more are saved, it would naturally be harder to increase multiplicatively. If everyone were saved, there would be no room left for growth. Even more inexplicable, Pentecost makes this argument despite the fact that the same parable in Mark’s gospel reverses the order of the increases (Mark 4:8)]
The Parable of the Mustard Seed
31He told them another parable: "The kingdom of heaven is like a mustard seed, which a man took and planted in his field. 32Though it is the smallest of all your seeds, yet when it grows, it is the largest of garden plants and becomes a tree, so that the birds of the air come and perch in its branches." (Matt. 13:31-32)
The New Scofield Reference Bible states that "[this parable] suggests the rapid but unsubstantial growth of the mystery aspect of the kingdom." I do not know what "rapid but unsubstantial growth" means. Pentecost provides a more detailed exegesis:
As the age progresses, several factors are to be observed. (1) The age is characterized by an abnormal external growth. That which was to be an herb has become a tree—it has developed into a monstrosity. (2) The monstrosity has become a resting place for birds [which are types of evil].203
Pentecost views the parable as teaching of large but cancerous growth, not large spiritual growth as taught by postmillennialists.204
The Parable of the Leaven
He spoke another parable to them, "The kingdom of heaven is like leaven, which a woman took and hid in three pecks of flour until it was all leavened." (Matt 13:33)
The New Scofield Reference Bible has an extensive commentary on this parable. In short, the flour is good and the leaven is evil, and so what is happening is pure church is ultimately corrupted by, once again, a kind of tumor of apostasy, a corrupting evil that begins small but eventually spreads throughout. Leaven, like birds, is said to be a type of evil, with reference to phrases such as "the leaven of the Pharisees." 205
Pentecost has this interpretation, which I am glad I din't make, but am happy to report:
The progress of the age is marked, according to this parable, (1) by the ministry of the woman. 206 This evidently refers to the work of a false religious system (Rev. 2:20; 17:1-8)….(2) The age is marked by the introduction of the leaven. This figure [leaven] is used in scripture to portray that which is evil in character… 207
In short, postmillennialists see the kingdom parables as promising slow but inevitable growth. Other's see them quite differently, with dispensationalists in particular arguing that they teach of the church being overcome by an unchecked increase of evil.
202 J. Dwight Pentecost. Things to Come, (Zondervan), 1958, p. 146.
203 Ibid., p. 147
204 Birds are not always types of evil, cf. Gen 1:20; Deut 14:20, Matt 6:26. And especially: Like birds hovering overhead, the LORD Almighty will shield Jerusalem; he will shield it and deliver it, he will 'pass over' it and will rescue it. (Is. 31:5)
205 Leaven is not always a type of evil, cf. Lev. 7:13; 23:17.
206 Um…, women are not always types of evil. Even within the restricted domain of the Kingdom Parables, cf. Matt. 25:1-13; Luke 15:8.
207 Pentecost, Things to Come, p. 148.