Exodus 40:3

3 Place the ark of the covenant law in it and shield the ark with the curtain.

Read Exodus 40:3 Using Other Translations

And thou shalt put therein the ark of the testimony, and cover the ark with the vail.
And you shall put in it the ark of the testimony, and you shall screen the ark with the veil.
Place the Ark of the Covenant inside, and install the inner curtain to enclose the Ark within the Most Holy Place.