It seems as if he wants to say here,
if I was born in the cradle of that common street porter,
I might have ended as somebody carrying the bags of other people.
And had he been born in another place then he might have become
the university professor.
The division of labor is not the outcome of different talents of human beings,
it is in many cases the breeding ground for
different careers that lead to the development of different talents.
In older theories, social stratification is often explained by
pointing at the different talents that people possess.
And people say some are physically strong but not too clever,
and others are intellectually well-endowed, etc., etc.
And that is what explains the social distance between the different ranks
of society, to quote Adam Smith, the differences in power and in wealth.
But Adam Smith here goes in the opposite direction.
He says people are born into a society with a certain preexisting division
of labor and their social location in that stratified social universe
determines in many cases the talents that they will develop later on in life.
Smith goes even so far here as to say that human beings differ
less from one another than the different breeds of dogs.