This is the 15888th most frequent Russian word.
проник
"Проник" means "penetrated" or "entered."
Here, 'проник' is used to indicate 'penetrating' or 'entering' into a space, often implying overcoming an obstacle.
Он проник внутрь здания через окно.
He entered the building through the window.
In this context, 'проникли' is metaphorically indicating that the words deeply affected or reached a profound emotional level.
Его слова проникли в самое сердце.
His words touched the deepest part of the heart.
Here, 'проник' is describing the action of light traveling through and reaching past the clouds.