In his Explanation of “The Living Flame of Love”, St. John of the Cross draws the Holy Mother of God as clearly as possible into the circle of his metaphor clarifying the mystical life.
Speaking of the shining of the Lamps of God in us and our intake of the divine Light, which means as much as participating in God’s characteristics and works, he says that this bears still another name, i.e. “to overshadow”.
And in connection to this, he reminds (us) that also the Archangel Gabriel called the exquisite privilege of Mary to conceive God’s Son, an overshadowing of the Holy Spirit [Cf. Lk 1:35].
If one wants to understand, the Saint thus follows, what is meant by that spreading of God’s shadow or that overshadowing or that shining, for all these expressions have an equal meaning, then one should remember that every creature evokes a shadow according to its own nature and capacity. A dark opaque object gives an obscure shadow: a bright translucent object a clear and transparent shadow.
Thus, the shadow of something dark will call forth a different darkness, darker to the extent that its cause is also darker, while the shadow of something bright will be light according to the nature of the original light.
Therefore, the shadow brought forth by the lamp of God’s beauty will be a different beauty, the shadow by the lamp of strength a different strength, etc. or better said, all these shadows will be the beauty itself, the strength itself of God, but in shadow, because the soul here on earth cannot perfectly understand or take God into itself.
Over Mary, the Holy Spirit came in all his fullness, and the power of the Most High overshadowed her in the most perfect way [Cf. The Living Flame of Love, III, 12].
Blessed Titus Brandsma
Mary’s motherhood of God, leading idea in the mystical life (excerpt)
Carmelrozen Vol. XX, May 1931, p. 11-15.
English translation provided by the Titus Brandsma Instituut Nijmegen
Titus Brandsma was born in the Frisian city of Bolsward, Holland, 23 February 1881
Saint John of the Cross writes in The Living Flame of Love, III, 12:
By what was said and what we shall now say it will be more plainly understood how excellent the splendors of these lamps are, for by another name they are called “overshadowings.” To understand this expression, it should be known that an overshadowing is the equivalent of casting a shadow; and casting a shadow is similar to protecting, favoring, and granting graces. For when a person is covered by a shadow, it is a sign that someone else is nearby to protect and favor. As a result the Angel Gabriel called the conception of the Son of God, that favor granted to the Virgin Mary, an overshadowing of the Holy Spirit: The Holy Spirit will come upon you and the power of the Most High will overshadow you [Lk 1:35].
John of the Cross, St. 1991, The Collected Works of St. John of the Cross, Revised Edition, translated from the Spanish by Kavanaugh, K and Rodriguez, O with revisions and introductions by Kavanaugh, K, ICS Publications, Washington DC.