T. S., Crewe. In reply to your question on Matthew 13:33: You will find it a rule in Scripture, that leaven is always used as typical of evil, whether in doctrine or practice; and this without a single exception. For instance, “Beware of the leaven of the Pharisees and of the Sadducees... Then understood they how that He bade them, not to beware of the leaven of bread, but of the doctrine of the Pharisees and of the Sadducees” (Matt. 16:6, 11, 12). See also Mark 8:15, Luke 12:1. In the last verse we read, “Beware ye of the leaven of the Pharisees, which is hypocrisy.”
Paul writes to the Corinthians, with regard to evil practice, “know ye not that a little leaven leaveneth the whole lump?” (1 Cor. 5:6). And to the Galatians, with regard to evil doctrine, subversive of Christianity, “A little leaven leaveneth the whole lump” (Gal. 5:9).
In Matthew 13:33, we are taught in one of six parables, which follow that of the sower, a similitude of the kingdom of heaven, in its new mysterious form, which was about to be brought into the world on the rejection of the King. For one peculiar and striking characteristic of the kingdom of heaven in mystery is that the King is not here. This was some of the “things new” which a scribe, instructed in the matter, would now bring out of his treasures, added to the “things old” which the prophets had aforetime written about the kingdom of heaven (Matt. 13:52). When it was said that it would be “as the days of heaven upon earth” (Deut. 11:21). And of the throne of the King, “His throne (should be) as the days of heaven” (Psa. 89:29). And again, the Gentiles should know that “the heavens do rule” (Dan. 4:26).
Now all this state of things was entirely set aside for the time, because of the rejection of the King —of Christ. And, instead of all the blessings consequent upon his reception, a state of things far different would be introduced. The enemy would come and sow tares amongst the wheat in the world, or, as it is called, “the field” (Matt. 13:38). The outward appearance the kingdom of heaven would then assume would be that of a vast sheltering power, under the figure of a tree, which would shelter the birds of the air, or as they are interpreted to be, the emissaries of the wicked one. (See Matt. 13:4,19,32). And again, as our parable tells us, doctrinal or moral evil would be introduced into the three measures of meal, or the sphere of the nominal profession of Christianity, till the whole should be leavened. One has only to lift up their eyes, with but a small amount of spiritual intelligence, on the state of Christendom around them, and see how fast this is coming to pass.
Words of Truth 1:220, 221.