# I was circumcised

"A priest circumcised me" 

# on the eighth day

"seven days after I was born"

# a Hebrew of Hebrews

Possible meanings are 1) "a Hebrew son with Hebrew parents" or 2) "the purest Hebrew".

# with regard to the law, a Pharisee

"as a Pharisee, I was committed to obeying all of the law"