Another parable spake he unto them; The kingdom of heaven is like unto leaven, which a woman took, an hid in three measures of meal, till the whole was leavened. Matthew 13:33.
(TDG 48.1)
When leaven is introduced into meal, it penetrates to every part, till an entire change takes place. So it is with the work of the Holy Spirit upon the human heart. The truth received and believed introduces new rules, new principles of action into the life. A new standard of character is set up—the life of Christ. Those who thus receive the truth depend on Christ, and they receive more and still more strength, and greater and still greater light. Daily they expel from their hearts vanity, selfishness, self-righteousness.
(TDG 48.2)
As they receive the spirit of Christ, light shines from them in clear, distinct rays. They have a solemn sense of eternal realities. There is a renewal of the entire mind and heart. As the leaven introduced into the meal leavened the whole, so the leaven of truth, if introduced into the heart, will absorb to itself all the properties of soul, body, and spirit....
(TDG 48.3)
Transformation of heart means an entire change of the entire man. “Except a man be born again, he cannot see the kingdom of God,” Christ declared (John 3:3). This change of heart is unseen; for it is an inward work, and yet, it is seen, because it works outward from within.
(TDG 48.4)
Has the leaven of truth been at work in your heart? Has it absorbed the whole heart, the whole affections by its sanctifying power? ...
(TDG 48.5)
Our first work is with our own hearts. The true principles of reform should be practiced. The heart must be converted and sanctified else we have no connection with Christ. While our hearts are divided, we shall never, never be fitted for usefulness in this life or for the future life. As intelligent beings, we need to sit down and think whether we are really seeking first the kingdom of God and His righteousness. The very best thing we can do is to think soberly and candidly whether we desire to put forth the effort necessary to obtain the Christian hope and secure the Christian’s heaven. If through the grace of Christ we decide that we do, the next question is: What is there that I must cut away from my life in order that I shall not stumble?—Manuscript 14, February 9, 1898, “Like Unto Leaven.”
(TDG 48.6)