# They serve a copy and shadow of the heavenly things

"They serve what is a vague image of the heavenly things" or "They serve what is only similar to the heavenly things". The words "copy" and "shadow" emphasize that the priesthood and the earthly temple were images of Christ, the true high priest, and the heavenly temple. 

# It is just as Moses was warned by God when he was about to construct the tabernacle

"It is just as God warned Moses when Moses was about to command the people to construct the tabernacle" 

# See that

"Make sure that"

# to the pattern

"to the design"

# that was shown to you

"that I showed you"

# on the mountain

"on Mount Sinai"