What idea did protestant revivalist charles grandison finney emphasize in his sermons?

The power of individuals to reform themselves.

Charles Grandison Finney (1792-1875) had been serving as an apprentice to become a lawyer, and was a rational young man who was not a big believer in faith.  But working in the law, he noticed that legal authors frequently quoted the Bible in commenting on principles of common law.  He was curious and purchased a Bible and began studying it in connection with references he found in legal writings.  He started going to a church, but felt awkwardly out of place there.  But then he told of a night (in October 1821, when he was 29 years old), where he said:  "A strange feeling came over me, as if I was about to die. I knew that if I did I should sink down to hell."  Early in the morning he headed to his office, and on the way he felt something in his mind that seemed to be confronting him with questions like, "What are you waiting for? What are you trying to do? Are you trying to work out a righteousness of your own?”  He came to the conclusion that spiritual salvation seemed to be an offer to be accepted, that all that was necessary on his part, was to give up his sins, and to accept Christ.  Finney recounted this story of his conversion moment in his memoirs, published in 1876. 

As an evangelist, Finney applied his own experience to others.  He led a movement in American revivalism that emphasized each individual's responsibility to make a decision to accept Christ.  Along with that ability to decide to become a Christian, Finney also emphasized ongoing responsibility to reform oneself, and in the process help to reform and perfect society as many individuals follow such a path of spiritual transformation.