en_tn/act/09/13.md

authority from the chief priests

It is implied that the extent of the power and authority granted Saul was limited to the Jewish people at this point in time. (see: rc://en/ta/man/translate/figs-explicit)

he is a chosen instrument of mine

"Chosen instrument" is an expression for being set apart for service. It can be translated as "I have chosen him to serve me". (See: rc://en/ta/man/translate/figs-metonymy)

for him to carry my name

"to carry my name" is an expression for identifying or speaking out for Jesus. It can be translated as "in order that he might speak about me." (UDB) (See: rc://en/ta/man/translate/figs-metonymy)

for the cause of my name

This is an expression for, "for telling people about me." (See: rc://en/ta/man/translate/figs-metonymy)