[source: Rerum Novarum, p. 

POPE LEO XIII SPEAKS OUT AGAINST USURY AND EXPLOITATION
[In Rerurm Novarum (1891), Pope Leo XIII wrote as follows:] "A 
devouring usury, although often condemned by the Church, but
practiced nevertheless under another form by avaricious and
grasping men, has increased the level of the evil; and in
addition the whole process of production as well as trade in every 
kind of goods has been brought almost entirely under the power
of a few, so that a very few rich and exceedingly rich men
have laid out a yoke almost of slavery on the unnumbered
masses of non-owning workers."
[source: Rerum Novarum, p. 60]

JUST OWNERSHIP OF MONEY DIFFERS FROM JUST USE OF MONEY
[The critical distinction made by Pope Leo XIII is that] "the
just ownership of money is distinct from the just use of
money."
[source: Rerum Novarum, p. 35]