John Gill Commentary Exodus 39:1

"And of the blue, and purple, and scarlet, they made finely wrought garments, for ministering in the holy place, and made the holy garments for Aaron; as Jehovah commanded Moses." — Exodus 39:1 (ASV)

And of the blue, and purple, and scarlet, they made cloths
of service
Jarchi observes that there is no mention made of linen, because these were not the priestly garments in which there was linen; but these were they with which they covered the vessels of the sanctuary when they journeyed; and so says Aben Ezra; and those were covered with cloths of blue, purple, and scarlet, (Numbers 4:5–15) though some think these were clothes wore by the priests:

to do service in the holy place :
and which they only wore when in it, and employed in the service of it; and therefore what follows must be by way of explanation:

and made the holy garments for Aaron, as the Lord commanded Moses ;
the particulars of which are given in the following verses.