ונתנו עליו כסוי עור תחש ופרשו בגד כליל תכלת מלמעלה
The Ramban observes that in the case of the other klei haMishkan, vessels of the Mishkan, they were first covered with wool and then covered over with the tachash – hide. The Aron HaKodesh was singular in that it was first covered with the tachash – hide and then was covered with the techeiles, turquoise wool. Chazal describe techeiles as having a color similar to that of the sea, similar to the sky which symbolizes the purity of Heaven. Thus, (according to Ramban) it was placed above the tachash – to call attention to the purity and sanctity of the…