Via press release from Courage International:
First, and most importantly, Jesus Christ is the Head of the Church, which is His Body, and the Spouse of the Church, which is His Bride. He has promised never to leave us abandoned (cf. John 14:18), to give us the Holy Spirit to teach and remind us what He has said (cf. John 14:26), and always to give his grace to Saint Peter and his successors so that they teach the rest of the Church clearly (Lk 22:32).
When one of those successors expresses his opinion in interviews and in similar ways, we ought to listen carefully and strive to understand and respect his judgment as our Holy Father. The pope knows, of course, that such comments are not the same as what is called the Magisterium, that is, the authority and responsibility to teach definitively on matters of faith and morals that the Lord Jesus entrusted to the pope and to the bishops in communion with him.
Our faith is firm that, when the pope and the bishops exercise the Magisterium and teach definitively, the Holy Spirit always guides them and prevents them from teaching erroneously. This is as true on the subject of sexuality, marriage and family as on any other topic of faith and morals. When and if the pope speaks more definitively on these issues, we rely on the Holy Spirit to ensure that he shares the truth clearly and consistently.
That truth — that God has established a unique context for the total gift of self that is reflected in sexual intimacy — is rooted in the nature of the human person, in the revealed Word of God, and in the consistent teaching of the Church. That sexual relations are only morally good in the context of a permanent, faithful marriage between a man and a woman whose relations are open to having children is a teaching that cannot and will not be changed by anyone.