We are bound to what we have freely chosen. This means that authentically human freedom is not freedom from commitment, but freedom to commit. And commitment entails responsibility for the consequences of one's choices. The fixed material world is the matrix for the exercise of human freedom. The institution of private property attaches pieces of the material world to particular moral agents.
Private property endows the spatio-temporal actions of individuals with moral significance.
This is true in at least three senses. First, private property allows the individual to be responsible for his own survival. Man is both spirit and body, and his physical existence requires certain material conditions to sustain it. The possibility of property places the responsibility for survival squarely on the individual's own shoulders. Obviously there can be no incentive for anyone to engage in productive labor if the fruits of that labor are liable to be plundered by his less industrious neighbors.