Why is Reverened Hale in Salem? its in the first act
Hale is in Salem because Parris has asked him to come. Hale is older and more experienced in identifying witchcraft.
Miller (in one of the many excerpts that interrputs the dialogue) writes that Hale was eager to come, it was "a beloved errand" and "he felt the pride of the specialist whose unique knowledge has at last been publicly called for."