They serve at a sanctuary that is a copy and shadow of what is in heaven. This is why Moses was warned when he was about to build the tabernacle: "See to it that you make everything according to the pattern shown you on the mountain."
NIV
[But these offer] service [merely] as a pattern and as a foreshadowing of [what has its true existence and reality in] the heavenly sanctuary. For when Moses was about to erect the tabernacle, he was warned by God, saying, See to it that you make it all [exactly] according to the copy (the model) which was shown to you on the mountain. [Exod. 25:40.]AMP
Who serve unto the example and shadow of heavenly things, as Moses was admonished of God when he was about to make the tabernacle: for, See, saith he, that thou make all things according to the pattern shewed to thee in the mount.
KJV