The severity of the sin, of the wrongdoing, is traditionally divided into two categories, venial sin and mortal sin. Mortal sin is the more serious of the two. Mortal sin is a conscious and freely chosen turning away from goodness, from the ultimate good and from God. It is a free rejection of our capacity to love and of our capacity to seek and find the truth. Mortal sin is a rejection of what we know to be the right thing to do in our conscience. In other words, it is a rejection of our very own dignity as beings created in the image of God. Such sins are called mortal because, in the language of the tradition, mortal sins lead to death and eternal damnation in Hell, unless the person sincerely seeks forgiveness. But one doesn't need to believe in Hell, or damnation, or eternal punishment to realise that the kinds of wrongdoings that are called mortal sin can have very serious and sometimes really deadly consequences for the flourishing of the whole community. For example, in the case of murder, in addition to the death of another person, there is significant trauma associated with suffering, anger, resentment, mistrust, fear, financial burdens and costs, disruption of work, destruction of families, and so on. There are specific conditions that must be met for a sin to be a mortal sin. First, it must be done with full knowledge; second, it must be freely chosen or willed, and third, it must concern grave or serious matter. Grave matter are those things that concern a fundamental good of the human person. Grave matter includes unjustifiably killing or physically harming a person, taking something that does not belong to you, having sexual relations with someone who is not your spouse, and withholding the truth from or deceiving people who have a right to certain information from you. In other words, a sin is only mortal in the strict sense when you freely choose to do it, knowing that it is the wrong thing to do. Of course, we are also very good at deceiving ourselves about what we really know, or finding ways to justify our behaviour to make it look like we didn't know or didn't choose. Being really honest with ourselves about these things is essential if we are going live whole-hearted, morally responsible lives. Whether a sin meets the strict definition of mortal sin or not intentions and actions must be wrong when they break down the kind of just and loving human community that God desires for us and that we really should desire for ourselves. Such actions break down the kind of community that we described in the previous section about Love, being free and being responsible means avoiding doing the wrong thing and trying sincerely to do the right thing for ourselves and for others.

Forgiveness, healing and reconciliation are important features of the Catholic perspective on sexual and relationship health. This is so for two simple reasons: First, God is love and we are created and called to be images of God; and second, we are all sinners, and that means we all almost inevitably find ourselves doing things that we know are not good for our own flourishing, or that we know hamper the flourishing of others. Our sinful actions damage the high quality of relationships characterised by love, justice, and chastity that God intended for human beings and indeed for human beings' relationship with God. Since God is love and God loves us so much that Jesus was prepared to die for us and for the truth that God wants us to live in a world of justice, peace and joy, God will forgive our sins. But, as free and rational beings, this forgiveness requires that we take responsibility for our sinful actions by sincerely acknowledging that what we did was morally wrong. Moreover, because we are free and created in the image of God who is just and merciful, we are also called to seek forgiveness from those we have harmed and in our turn forgive those who have harmed us. This is why, in the prayer that Jesus teaches his disciples, 'the Lord's Prayer' or the 'Our Father', we ask God to forgive our sins (debts or trespasses) as we forgive those who sin against us (Matthew 6: 9-13). As Pope Francis has said, Listen carefully to this: each of us is capable of doing the same thing that that man or that woman in prison did. All of us have the capacity to sin and to do the same, to make mistakes in life... Mercy overcomes every wall, every barrier... And it is mercy which changes the heart and the life, which can regenerate a person and allow him or her to integrate into society in a new way (Pope Francis, 2014). The United States Conference of Catholic Bishops (1991) makes a similar point and contextualises it in the liturgical and sacramental life of the Church: 'We are aware of our own frailty and sin as well as God's abiding presence and promise of forgiveness. As members of the Church, we draw strength, comfort, and renewed challenge from the Word of God, the Eucharist, and the healing and strengthening power of the sacrament of reconciliation.' Central to Jesus' message was that God unconditionally loved every human being and that this love is not conditional on 'being good'. This love cannot be earned, and no matter what human beings do, they cannot prevent God's love being available to them. Jesus taught that God would unconditionally forgive anyone who showed any sign of wanting to come to him and that real love always forgives... In many cases, the weakest and most vulnerable human beings are those who have difficulty in accepting themselves and their sexuality, and these are the people to whom the Church, if it is following Christ, should show the most love, commitment and understanding... None of us can or should condemn others (Vardy 1998, pp. 224-225). Though we might help others to see the truth of the moral wrongness of their actions, we cannot condemn them as human beings, who, like us, are seeking to live a meaningful life in a morally complex world. If we condemned people as human beings because of their sinful actions then forgiveness would be impossible. Forgiveness and healing are possible precisely because the Catholic tradition emphasizes an essential difference between the person, eternally loved by God, and the moral behaviour of that person. Our moral behaviour may change the way we relate to God, but it never changes how God loves us. As Vardy (1998, p. 225) points out, our task is to strive daily to align our moral behaviour with the belief that we, all human beings, and all of creation, are created and loved by God, who desires only our flourishing and happiness. Our task is to progress on our life's journey and, as we do so, to help our fellow travellers with care, compassion and understanding.