וְשַׂמְתָּ֤ אֹתוֹ֙ עַל־פְּתִ֣יל תְּכֵ֔לֶת וְהָיָ֖ה עַל־הַמִּצְנָ֑פֶת אֶל־מ֥וּל פְּנֵֽי־הַמִּצְנֶ֖פֶת יִהְיֶֽה׃
And thou shalt put it on a thread of blue, and it shall be upon the mitre; upon the forefront of the mitre it shall be.
Read kabbalistic (mystical) interpretation of Exodus 28:37: and classical mystical sources.