6 However, the conclusions arrived at by the commission could not be considered by Us as definitive and absolutely certain, dispensing Us from the duty of examining personally this serious question. This was all the more necessary because, within the commission itself, there was not complete agreement concerning the moral norms to be proposed, and especially because certain approaches and criteria for a solution to this question had emerged which were at variance with the moral doctrine on marriage constantly taught by the magisterium of the Church. Consequently, now that We have sifted carefully the evidence sent to Us and intently studied the whole matter, as well as prayed constantly to God, We, by virtue of the mandate entrusted to Us by Christ, intend to give Our reply to this series of grave questions.
Source: Humanae Vitae (Vatican.va)