What is your interpretation of the significance of the New Deal in terms of its break with the past, its effect on the people it was designed to help, and its impact on the future course of history?

Before the New Deal, the vast majority of economists followed classical principles where the market was the absolute king and it determined the well being of the entire economy. The New Deal introduced the world to new economic concepts which we call Keynesian economics, and those concepts had a huge impact in all the world.

I personally disagree with classical or neoclassical economists not because their theory is wrong, but simply because classical economics exclude the human factor out of the economic equation. Classical economics state that individuals will always pursuit their best interest and will try to maximize their utility while minimizing their costs. Theoretically it is correct, but human nature is more complex than utility maximization. E.g. everyone knows that alcohol, drugs, smoking and many other vices are wrong and hurt you, but their supply has never decreased and it is constantly increasing.

The New Deal basically supported increasing government spending in order to boost the economy, which is something common nowadays but back then was a heresy for economists, something completely irrational and insane. But it worked, and it also worked when it applied in Europe after WWII as the Marshall Plan. The advantage of Keynesian or neo-Keynesian economics is that works in real life, while classical or neo-classical economics never work in real life.