What is an explanation of "If you can once engage people's pride, love, pity, ambition, (or whatever is their prevailing passion) on your side, you need not fear what their reason can do against you." Using modern language ?
The quote is from Philip Stanhope, Fourth Earl of Chesterfield, simply known as Lord Chesterfield. The premise of the quote is about passion and its ability to obscure reason. If we are to paraphrase it in simpler language it might be summed up as such: If you can get people passionate for you, then you do not have to be afraid they will use logic against you.
The truth of statement has been shown time and again throughout history from religious cults to tyrannical dictatorships. Passion for a subject, thought or idea can override logic, reason and facts.
This is because humans are designed to feel and express emotions. That is why the quote is not only accurate psychological, but physiologically as well. Facts must be remembered to be useful, reason (or logic) must be studied to be applied, but emotions are natural. Emotions require no thought, no remembering and can be applied without thought. Therefore, by plying people's emotions an influencer can bypass the harder aspects of thought.