“The kingdom of heaven is like unto leaven, which a woman took, and hid in three measures of meal, till the whole was leavened” (Matt. 13:3333Another parable spake he unto them; The kingdom of heaven is like unto leaven, which a woman took, and hid in three measures of meal, till the whole was leavened. (Matthew 13:33)). Here we find that there would be the spread of doctrine within, assimilating to itself whatever came in its way. “Leaven” is used in the Gospel of Matthew, as well as occasionally elsewhere, for doctrine. The three measures of meal are not legitimately assumed to mean the whole world; they are, I suppose, a certain defined space devoted to the action of the leavening doctrine, throughout which the doctrine spreads effectively. Whenever “leaven” occurs symbolically in the Word of God, it is never employed save to characterize corruption which tends to work actively and spread.
I believe that the leaven here sets forth the propagandism of dogmas and decrees, after that Christendom became a great power in the earth (answering to the tree, which was the case, historically, in the time of Constantine the Great). We know that the result of this was an awful departure from the truth. When Christianity grew into respectability in the world, instead of being persecuted and a reproach, crowds of men were brought in. A whole army was baptized at the word of command. Now the sword was used to defend or enforce Christianity; no doubt it was thought that earthly reward and imperial favor might quicken the downfall of heathenism. All this prepared the way for the spreading of the leaven, but not for the sound truth of God, nor for His grace.
W. Kelly (adapted)