In June 1733 he travelled to Scala to aid a friend at a mission at Ravello and he met up with and became one of the earliest companions to Liguori in founding the Redemptorists which he joined in 1733. The pair worked together and gave missions along the coast of Amalfi from 1735 to April 1736 (Easter; missions in Salerno and Amalfi) when Sarnelli's health started to decline. He had to return to Naples where he spent the next decade in a poor apartment with one religious as a companion. In 1841 he prepared for the planned canonical visitation of Cardinal Giuseppe Spinelli and participated in missions at Casali. Having become aware of the rampant corruption of young women, he decided to direct all his work against prostitution. But doing this work earned him threats from the criminal element that made profit from this. In April 1744 he stopped preaching altogether because his health became so dire.