Today (20 December) is the U.N. 'International Human Solidarity Day', a day which reminds us about the importance of solidarity for the achievement of the international agreements. In his 1987 encyclical 'Sollicitudo Rei Socialis', Blessed John Paul II described solidarity as a 'Christian Virtue'.
Click here to read a summary of 'Sollicitudo Rei Socialis', in which JPII challenged Christians everywhere to fight for solidarity. You can read the full text of the encyclical on the Vatican Website.
"Solidarity is undoubtedly a Christian virtue. In what has been said so far it has been possible to identify many points of contact between solidarity and charity, ... In the light of faith, solidarity seeks to go beyond itself, to take on the specifically Christian dimension of total gratuity, forgiveness and reconciliation ... Beyond human and natural bonds, already so close and strong, there is discerned in the light of faith a new model of the unity of the human race, which must ultimately inspire our solidarity ... Solidarity therefore must play its part in the realization of this divine plan ... The "evil mechanisms" and "structures of sin" of which we have spoken can be overcome only through the exercise of the human and Christian solidarity to which the Church calls us and which she tirelessly promotes. Only in this way can such positive energies be fully released for the benefit of development and peace." Blessed John Paul II, 1987