Jesus compares the kingdom of God with the parable of the leaven: "He told them still another parable: The kingdom of heaven is like yeast that a woman took and mixed into about sixty pounds of flour until it worked all through the dough" Mattthew 13:33, this parable is also in Luke 13:20-21.
Jesus when he teaches us about the parable of the leaven he is referring to the nature of the good. All the spiritual gifts are good by definition. Thomas Aquinas in his book Summa Theologiae explain that the spiritual gifts are perfections: "Be perfect, therefore, as your heavenly Father is perfect", Matthew 5:48. Everything that is perfect is also Good: "every good gift and every perfect gift is from above" James 1:17
Aristotle explain in his book metaphysics that something is perfect when it cannot be surpassed, overcome or improve in its genre. For example in the genre of the segments of time, we have this day, this year. What is the perfection? The perfection is the eternity: the possesion of all time, present, past and future. God is eternal, the eternity is a divine attribute. When a perfections of God is transmissible to man, we say that perfection is a gift, like the mercy, the wisdom or the piety.
God is the source of the good, the good is a nature and a spiritual gift: "Why do you call me good?" Jesus answered. "No one is good - except God alone".
The good is a nature because every being tends to his own good or perfection, the fruit is good when it is mature. This is the reason why the spiritual gifts are progressive like the leaven.
The parable of the leaven when is compared with the kingdom of God emphasizes progressivity and progressive thinking, the spiritual gift of knowledge.
The kingdom of God is fundamentally progressive because it explains the transformation of man towards his true nature: the conformity to God, the spiritual maturity.
The kingdom of god is the empire of wisdom, the kingdom of perseverance, the government of piety and godliness. The kingdom explain to us that we have to choose between good and evil, between the spirit and the flesh, between god and money. In essence the kingdom of God consist in how to live ethically.
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