The priestly garments of the Kohanim, have a mystical and mysterious side to them. The four garments of the regular Kohein (pants, belt, shirt, and hat), were not nearly as impressive as the eight garments of the Kohein Hagadol.
It can be said, that there was a dramatic change in history, because of these sacred garments. It is told that Alexander the Great had a dream that he would meet the High Priest in his eight garments. The dream actually came true when Alexander met the Kohein Hagadol, known as Shimon Hatzaddik.
To paraphrase a famous movie, this was the beginning of a beautiful friendship. Alexander became a faithful friend to the Jews, as he went about conquering the world.
To this day, many Jews name their children, “Alexander or Alexandra,” as a tribute to this friendship.
The mystical aspect of these garments is that they served as atonement for various. Just looking at them, had an effect on that individual.
The חושן משפט, or the breastplate served to atone for injustices in the courts. It also atoned for impure thoughts in the heart.
The מעיל, or outer garment, atoned for Lashon Hara, improper speech. The מכנסי בד, the linen trousers, atoned for sexual immorality.
In general, the establishment of these garments, was meant to help overcome the stubbornness of the Jewish people. It was mainly to emphasize the importance of humility, and serving G-d humbly.