Archbishop Vincent Nichols, preaching at Midnight Mass, cited various examples of ways in which people needed to be purified in order to "become partners with God".
In his homily he reflected on the meaning of the incarnation, saying it enabled work and human love to be seen as a taking part in the creativity and creative love of God.
However he cautioned against various practices that fell short of the standards he said God was looking for.
He cited charity motivated by self-interest, exploitative patterns of business, as well as sexual expression "without the public bond of the faithfulness of marriage and its ordering to new life".
He went on: "Even governments mistakenly promote such patterns of sexual intimacy as objectively to be approved and even encouraged among the young."