“Because, even because they have led my people astray, saying ‘Peace', and there is no peace. And when someone builds up a flimsy wall they daub it with whitewash.”
The word for whitewash comes from a root meaning to talk nonsense. Some in Israel have built up for themselves ideas, empty hopes, which are the equivalent of a flimsy wall which will not stand the test (compare Ezekiel 13:5 and Ezekiel 13:16) and the prophets contribute to their folly by whitewashing it to hide the cracks. What they speak is nonsense. They declare peace, but there will be no peace. They promise safety and prosperity for Jerusalem when there will be no safety or prosperity. Thus they lead the people astray.
It is always a temptation to a preacher to speak what people wish to hear, to reinforce their prejudices, to make them satisfied with a low level life and a lesser morality. They please men and not God. But such preachers too will be disqualified by God from His purposes. If we never disturb people we must question our ministry.