"The community of believers was of one heart and mind, and no one claimed that any of his possessions was his own, but they had everything in common."
For this reason, it has been an easy move for many Christians in the past 150 years to adopt a kind of de facto socialist point of view. However, already by the fourth century, and probably much earlier, Church Fathers were pointing out that this ideal from Acts was only lived in monastic settings, where in addition to a promise of poverty, monks and nuns also vowed celibacy. Marriage, being an institution of God for those in the world and not in monastic communities, necessitates the ownership of private property, which allows for parents to produce goods for the benefit of those who are helpless to do so for themselves, namely for children. Thus it is that Pope Leo XIII can write:
"it is clear that the main tenet of socialism, community of goods, must be utterly rejected, since it only injures those whom it would seem meant to benefit, is directly contrary to the natural rights of mankind, and would introduce confusion and disorder into the commonweal. The first and most fundamental principle, therefore, if one would undertake to alleviate the condition of the masses, must be the inviolability of private property. This being established, we proceed to show where the remedy sought for must be found."
He also makes the interesting exegetical argument that God Himself ordained private property, by noting that the commandment, "Thou shalt not covet," makes no sense if what someone else has to be coveted is in fact common property.
Finally in this section of Rerum Novarum (11-15), the pope accurately predicts the drying up of capital (=means of production) in communist states (as Koz noted in a recent comment on the current state of Polish labor) when he writes:
"the sources of wealth themselves would run dry, for no one would have any interest in exerting his talents or his industry; and that ideal equality about which they entertain pleasant dreams would be in reality the levelling down of all to a like condition of misery and degradation."
It is worth noting that in both quotes, the interest of the Holy Father is in the alleviation of poverty, one of the Church's main projects while in the world. Thus, we see that the 'preferential option for the poor', is not an invention of Vatican II or socialists, but is inscribed in the very nature of the Church. However, when it comes to proposals on how to carry this out, the Church's preferential option, as we shall see, is realistic in the sense that it acknowledges the shortcomings of actual people and the need therefore of justice. The traditional definition of justice is the virtue of giving each person his or her due. In the area of our material existence, this means the preservation of justly acquired capital in the hands of the laborer who created it.