Complex sentence: Mainly because of its prohibition of all forms of artificial contraception, the encyclical was politically controversial, but it affirms traditional Church moral teaching on the sanctity of life and the procreative and unitive nature of conjugal relations.
Split into simpler sentences: Mainly because of its prohibition of all forms of artificial contraception, the encyclical was politically controversial. It affirmed traditional Church moral teaching on the sanctity of life and the procreative and unitive nature of conjugal relations.