I found a passage from St. Faustina's Diary in which Jesus describes the chosen souls who are hidden but shine brilliantly, dispelling the darkness.
The Lord has given me to know how much He desires the perfection of chosen souls.
Chosen souls are, in My hand, lights which I cast into the darkness of the world and with which I illumine it. As stars illumine the night, so chosen souls illumine the earth.
And the more perfect a soul is, the stronger and the more far-reaching is the light shed by it.
It can be hidden and unknown, even to those closest to it, and yet its holiness is reflected in souls even to the most distant extremities of the world. (Diary 1601)