# chosen from among people

"whom God chooses from among the people" 

# is appointed

"God appoints" 

# to act on the behalf of people

"to represent the people"

# so that he may offer

The word  "he" refers to a high priest. The writer describes the sinfulness of the Old Testament priests, and then he shows that Christ has a better kind of priesthood, one not based on Aaron's priesthood but on the priesthood of Melchizedek.