What the Rav said:
Rabbi Menachem Mendel of Rimanov says, ‘What’s the meaning of the expression, “nasata v’natata b’emunah [did you conduct your business with Emuna]”?
This means that all day long you need to think about and be busy with Emuna.
For example, if I move my hand, that’s Hashem. Everything is Hashem.
Think all day long about ways of not removing your thoughts from Hashem, not even for a moment.
That’s the meaning of “doing business” – that you should busy yourself in how you can live constantly with Emuna.
My thoughts:
There are six permanent commandments that a Jew is meant to observe all day, every day.
Five out of six of these perpetual obligations are related to having Emuna in Hashem (see here for more info on this: https://outorah.org/p/6284/).
The Rav explains here how we can do this in practice.
Just like (l’havdil) a person can spend all day long thinking about their business, what’s going on with their business, what can they do to improve their business, how to make more money from their business, etc, etc – so, too a person can actually think about Hashem all day long too.
How? By seeing Hashem in everything I do all day long and by noticing that Hashem is actually doing everything (both the things I like and the things I don’t like).
That way, I’m ‘busying myself’ with Hashem, and I’m fulfilling perhaps even five of those six permanent commandments!