והיה על המצנפת אל מול פני המצנפת… (תצוה כח:לז)

Chazal say that the function of the “מצנפת” – turban – was to atone for the sin of גאוה – haughtiness.  However, when it comes to כבוד שמים – to uphold the honor of Hashem – it is a mitzvah to be haughty about it.  Therefore the words “קודש לשם” were engraved on the ציץ, to show that when it comes to honoring Hashem one is allowed to be filled with pride – as it says “ויגבה לבו בדרכי השם” – and his heart rose to go in the ways of Hashem.