Leviticus 16:4

He shall put on the holy linen coat Upon other days, when the high-priest officiated, he was bound to put on all the garments mentioned Exodus 28:4, four of which were called golden garments, because there was a mixture of gold in them; but on this day he put on only the four linen garments here specified, which were common to him with the ordinary priests. The reason whereof was, that this was not a day of feasting and rejoicing, but of mourning and humiliation, at which times people were to lay aside their ornaments. At this solemn season the high- priest was to wear nothing but linen, and that probably not only in token of humiliation, but also because it is a more proper emblem of purity than woollen, as it is more easily cleansed, and washes whiter. These are holy garments Peculiarly so; to be used only when he was in the exercise of this solemn part of his sacred office. Therefore shall he wash his flesh in water Besides the washing of his hands and feet, as upon other days, at the beginning of the service, the high-priest was, on this day, to wash his whole body before he put on these holy garments, and entered on the solemn service of the day; which significant rite fitly betokened that peculiar holiness and purity which become all that approach God in his worship, and especially all that minister in holy things.