29 Now it is an outstanding manifestation of charity toward souls to omit nothing from the saving doctrine of Christ; but this must always be joined with tolerance and charity, as Christ Himself showed in His conversations and dealings with men. For when He came, not to judge, but to save the world, (41) was He not bitterly severe toward sin, but patient and abounding in mercy toward sinners? Husbands and wives, therefore, when deeply distressed by reason of the difficulties of their life, must find stamped in the heart and voice of their priest the likeness of the voice and the love of our Redeemer. So speak with full confidence, beloved sons, convinced that while the Holy Spirit of God is present to the magisterium proclaiming sound doctrine, He also illumines from within the hearts of the faithful and invites their assent. Teach married couples the necessary way of prayer and prepare them to approach more often with great faith the Sacraments of the Eucharist and of Penance. Let them never lose heart because of their weakness.
Source: Humanae Vitae (Vatican.va)