Musar zu Schemot 28:31

(Shemoth 28:31): "And you shall make the me'il of the ephod [i.e., belted by the ephod] entirely of blue wool [tcheleth]." It would seem that tcheleth was necessary because of what our sages of blessed memory have said about tzitzith (Menachoth 89a), that tcheleth is reminiscent of [the color of] the sea; the sea, of the firmament; and the firmament, of the Throne of Glory. That is, he shall remember thereby that he will come before the Throne of Glory. Similarly, in our instance. It is stated in Tanna d'bei Eliyahu, that the lashon hara that one speaks ascends opposite the Throne of Glory, as it is written (Psalms 73a): "They have placed their mouths in the skies, and their tongue walks the earth." Since he is clothed in tcheleth, he will remember and reflect upon whither his words ascend, and he will guard himself against this.