To the pope as to all his predecessors, marital relations are much more than a union of two people. They constitute a union of the loving couple with a loving God, in which the two persons create a new person materially, while God completes the creation by adding the soul. For this reason, Paul VI teaches in the first sentence of Humanae vitae that the transmission of human life is a most serious role in which married people collaborate freely and responsibly with God the Creator. This divine partnership, according to Paul VI, does not allow for arbitrary human decisions, which may limit divine providence. The Pope does not paint an overly romantic picture of marriage: marital relations are a source of great joy, but also of difficulties and hardships. The question of human procreation exceeds in the view of Paul VI specific disciplines such as biology, psychology, demography or sociology. The reason for this, according to Paul VI, is that married love takes its origin from God, who "is love". From this basic dignity, he defines his position: