Preaching and heart change

Adrian Warnock has more to say on preaching to change the mind and heart. He quotes George Whitefield in saying that true conversion is of the heart, not of doctrine and actions. Adrian then makes this observation:

These words are terrifying- a man can be apparently a Christian but never really saved. All this might leave us tempted to give up preaching at all, and leave it all to God since conversion is a sovreign act. And yet, God has also ordained the means. The mystery is that he has determined that the spoken word of God would have the primary place in being the tool by which genuine transformation can occur.

During the past few decades I've heard a lot preached, written, and broadcast about how easy it is to be saved, and how little heart transformation is expected of us. Yet when I read the works of preachers from, say, a hundred years ago back to the time of the apostles, they have a lot more to say about conversion of the heart. Could we be missing something?