Albert Barnes Commentary Hebrews 9:3

"And after the second veil, the tabernacle which is called the Holy of holies;" — Hebrews 9:3 (ASV)

And after the second veil. There were two veils for the tabernacle. The one which is described in Exodus 26:36-37 was called the hanging for the door of the tent and was made of blue, purple, scarlet, and fine-twined linen, suspended on five pillars of shittim-wood overlaid with gold. This served as a door for the whole tabernacle.

The second or inner veil, referred to here, divided the holy from the most holy place. This is described in Exodus 26:31-33. It was made of the same materials as the other, though it would seem in a more costly manner and with more embroidered work. On this veil, the figures of the cherubim were intricately worked. The design of this veil was to separate the holy from the most holy place; its symbolic meaning is clear, for the apostle Paul himself explained it in this chapter (Hebrews 9:8 and following).

The tabernacle. That is, the inner tabernacle, or that which was more properly called the tabernacle. The name was given to either of the two rooms into which it was divided, or to the whole structure.

Which is called the Holiest of all. It was called "the Most Holy Place," "the Holy of Holies," or "the Holiest of all." It was called this because the symbol of the Divine Presence—the Shekinah—dwelt there between the cherubim.