Why do they comment on the goats'-hair curtains and not on the lower curtains of wool and linen, which the Torah mentioned first - in Pasuk 8, and which they placed on top of the Kerashim, and the goats'-hair curtains covered them! Moreover, they did not erect the Mishkan until the Milu'im (a week before Rosh Chodesh Nisan), when there were also sockets to hold up the Kerashim. Perhaps the curtains were used to cover the Kerashim once they were made, and still lying on the ground. However, Da'as Zekenim says 'to be an Ohel on the Mishkan immediately.' This requires investigation (PF). See note 2.

See note 1. Bear in mind that the bottom curtains were made as a cover - and the Kerashim, to hold up the bottom curtains, which were called 'Mishkan', as the Torah wrote in Terumah, 26:1. since that question remains however, why Hashem did not instruct Moshe to make the goats-hair curtains before the 'Mishkan' in order to cover them immediately (and not the Kerashim) - since that was their main function, as implied by the words "le'Ohel al ha'Mishkan". Refer to 36:14:2:1.