An encyclical written by 2 popes: 'Light of Faith' explores faith as service to truth, society

Pope Francis has issued his first encyclical, a meditation on faith that is unique because it was largely written by someone else: Benedict XVI.

Benedict's hand is evident throughout the first three chapters of "The Light of Faith," with his theological style, concerns and reference points clear.

Francis' priorities come through in the final chapter, where the Argentine Jesuit insists on the role of faith in serving the common good and giving hope to those who suffer.

Francis acknowledges in the encyclical released Friday that he merely "added a few contributions of my own" to Benedict's "fine" first draft, which he left unfinished when he retired. Together, the two popes crafted the final installment of Benedict's conceived trio of encyclicals on the three Christian theological virtues: charity, hope and faith.