Translated excerpts from the book:
Στεργίου Ν. Σάκκου [Read CV], «Λάμψον καὶ ἡμῖν...», ἐκδ. «ΧΡΙΣΤΙΑΝΙΚΗ ΕΛΠΙΣ» ΟΡΘΟΔΟΞΗ ΑΔΕΛΦΟΤΗΤΑ, Θεσ/νίκη 2023.

Spiritual Transfiguration (part 2)

  “Resist the devil and he will flee from you,” exhorts James, the brother of the Lord (4:7). We need a spirit of resistance in order to live in this world without falling under the power of its ruler. It is telling that our Lord Jesus Christ, shortly before His departure from this world, prayed for His disciples, asking His Father: “I do not pray that Thou shouldest take them out of the world, but that Thou shouldest keep them from the evil one” (Jn 17:15). He does not pray for them to be taken out of the world, but that they may be guarded from the evil one. Christians will live in the world, interact with it, cooperate with it, and yet guard themselves from the influence of the evil one. 
  To the command, “Do not be conformed,” the God-inspired Apostle adds, “but be transformed.” The faithful are called not only to refrain from being conformed to this world, but also to be continually transformed in spirit. This implies a constant spiritual perfecting and growth. A standstill is never a good sign—either in the physical life or in the spiritual one. Saint Theophylact gives this counsel: “Do not say, as Peter did, ‘Lord, it is well that we are here’; for one must always make progress and not remain at one level of virtue and contemplation, but move forward elsewhere.” Spiritual advancement—spiritual transformation—is an essential mark of the Christian life.
  But how is this vital spiritual transformation attained? The apostle Paul answers: through renewal. In the mystery of Baptism, we were spiritually reborn. We renewed this rebirth of Baptism when we willingly made the decision to belong to Christ—that is, to be conscious members of the Church. Yet that initial renewal is not enough. We must continually renew ourselves spiritually—we must undergo a constant renewal. Saint John Chrysostom advises: “This is exactly what we do with our homes—we are always tending to them when they grow old—do the same with yourself! Have you sinned today? Have you aged your soul? Do not despair, do not lose heart, but renew it through repentance, tears, confession, and acts of mercy—and never cease to do this.” When we neglect to renew ourselves, we begin to lose the battles of the spiritual life.
  More specifically, the apostle Paul speaks of the renewal of the mind—that is, of our thoughts, our inner mindset. Through the mystery of Baptism, we have put on Christ (see Gal 3:27) and have been given “the mind of Christ” (1 Cor 2:16) — “Have this mind among yourselves, which is yours in Christ Jesus” (cf. Phil 2:5). Yet through sin the mind becomes clouded, worn down by the passions, aged by vice. “Nothing ages the soul and the body as much as sin,” observes Oecumenius.
  This is why we are in constant need of renewal of the mind. “Before all else, our judgment about things must be sound,” teaches the golden-tongued Father. “And even if we do not yet practice virtue, let us at least praise it; and even if we have not yet turned away from evil, let us still condemn wickedness. In this way, we will form upright judgments—and  by progressing in this way, little by little, we will also come to put virtue into practice.”
  But how, then, is the human mind renewed? Through the truths of the Gospel. Just as the intellect is shaped and instructed through study, so too is the mind reshaped, purified, and illumined through the study of the Holy Scriptures—through the sacred writings. It becomes new, filled with holy thoughts, pure desires, and noble affections. In a homily for the Feast of the Transfiguration, Saint Gregory Palamas urges: “Now pay attention, I ask you, and lift up the eyes of your mind to the light of the Gospel message, so that you may at last be transformed through the renewal of your mind!”
  Once the mind has been renewed, it acquires the precious virtue of discernment—the ability to recognize what the will of God is in every situation: “that you may prove what is the will of God, what is good and acceptable and perfect.” (Rom 12:2) “Discernment is greater than all other virtues,” teaches Saint Isaac the Syrian. With discernment, the believer sees all things in the light of eternity —to see with the very eyes of God. He comes to know the divine will and strives to live it out in his daily life, submitting himself to the command spoken by the heavenly Father at the Transfiguration: “Listen to Him.” (Mt 17:5) Through this obedience, he is continually refined, uplifted, and spiritually transformed.