At a young age, Jace learned that a word repeated enough times would lose all meaning. It would become sound, having nothing within it: senseless, vacant, hollow noise. Just the moving of lips and the vibration of air.
He tried it out on miscellaneous things near and within the Wayland manor: fork, mirror, lake, et cetera. It was easy; these items had no emotional value for him, and the words lost identity rather quickly.
After his father died and he moved to the New York Institute, he would lay awake at night listening to Maryse sing Alec to sleep, dispelling his fears of the dark. While he listened, he repeated a different set of words: family, home, parent. He repeated until his grief wore away, clutching his tiny toy soldier.
After he realized Clary was his sister, he had no comforting voice to sing away his fears, no small toy to help brave his despair. He still vigilantly repeated, the words changing again: sister, lover, belonging. Only this time, his pain and guilt never wore away. Each time he repeated, the ice-words thrust daggers into his chained heart, like slivers splintering from his tongue as he whispered.
The new assemblage of phrases only reminded him of flaming hair, eyes of pine-forest green, and skin like creamy white china. The sound was never hollow or vacant, for Clary would never lose identity in his heart. To Jace, she would never be anything less than the most meaningful thing in the world.