What's the meaning of 'sorry lot' in Albert Einstein's quote?

I just came across this quote by Albert Einstein when I was leafing through the book 'Super Cooperators: Altruism, Evolution, and Why We Need Each Other To Succeed':

If people are good only because they fear punishment, and hope for reward, then we are a sorry lot indeed

What does 'sorry lot' mean here?

I'm thinking sorry might mean pathetic/sad/loser and lot means group. Am I right?

A sorry lot (sorry definition 2, lot definition 4) is simply a regrettable or deplorable lot; so a regrettable group. It is the same as saying a sorry bunch. It could potentially be interpreted as pathetic, but not usually. So you are correct; it means a sad group.

Note that sad does not mean that the members of the group are sad (emotionally), it means that the group as a whole is sad. Definitions 3 and 5 both apply.

Wow, I had no idea that the phrase goes back that far but I hear this today in casual Australian speech.

Here, it can indeed mean a sad bunch of people but you could use it to refer to other types of groups as well.

For example, a conservative person might say that unemployed people on the pension are 'a sorry lot'. (Of course, I'm not suggesting for a moment that this is the case!)

Alternatively, you might hear a teacher saying to rebellious students, 'You're a sorry lot, you kids!'

Perhaps, at work, I might refer to a group of arrogant customers as 'a sorry lot'.

I'm not going on any dictionary-esque definition but this is based on how the word is used in everyday Australia. I suppose that you could sum it up in saying that somebody will say it about a group that they consider to be misfortunate or inferior (among other things).

I think that the previous answer is certainly correct but I suggest that the definition is wider in scope. 'Sorry' and 'lot' don't need to be translated individually and literally as it is the two words together that create the meaning of the phrase. I have no evidence to support this, as yet, but I see the phrase as an idiom.

Basically ditto Rachel but let me say it a little differently.

"Sorry" can mean bad or undesirable in general. Like if you say, "The washing machine is in a sorry condition", you mean that it is worn out or not working well.

"Lot" as a noun means a group of things considered as a unit. Like, "We ordered three lots of pencils." The retailer sells pencils in "lots", and we bought three of them.

So "a sorry lot" is a group of something that is not in good condition. It can be applied to objects, but I think is most often used to describe a group of people. When used about people, it can refer to conditions that are their own fault, or not. Like, "The refugees were sick and exhausted from their long journey. They were a sorry lot." But also, "Before I moved to this town I didn't realize that the people were all rude, selfish, and stupid. They are a sorry lot."