Today the Scottish Episcopal Church, meeting in its General Synod in Edinburgh, takes the first step in a process which may lead to same sex couples being able to marry in our churches and to our clergy being able to enter into same sex marriages. It is a two-year process. In 2016, the voting needs to produce a simple majority in each of the three 'houses' – laity, clergy and bishops. The second and final stage in the process will be reached in 2017 when two-thirds majorities will be needed in each house,

What is proposed is a simple alteration to our Canon – or church law – which governs marriage. The Canon at present defines marriage as being between a man and a woman. That definition would be removed and a conscience clause would be added which makes it clear that none of our clergy would be obliged to conduct a wedding against their conscience.

The journey to this point has been long and challenging. We committed ourselves to a church-wide talking process - facilitated conversation which allowed all views to be expressed in a safe environment. We have experienced considerable internal dissension. If we approve this change, we shall suffer some 'consequences' or sanctions from within the Anglican Communion. Those sanctions would be imposed in an attempt to hold together a Communion which stretches from liberal America to deeply conservative sub-Saharan Africa.

More painful is the fact that this is an issue where the mind of the church cannot be decided by voting alone. Those who believe that this move would be wrong and sinful will continue to hold that view no matter what the General Synod decides. That is why the major challenge facing our leadership is that of preserving the unity of our church. The General Synod will make a decision. But that decision will not change the reality that we shall continue to be a church which expresses diversity to the point of division on this issue. When a vote is taken and a decision declared, the 'other view' will not just disappear as if voted out of existence. It must continue to be recognised and honoured in our life.

You could be forgiven for wondering why human sexuality issues are so difficult for churches. After all, our society seems to have been able to deal with the same-sex marriage question without major difficulty. Massive and very rapid social change has been taking place. Legislation to permit same-sex marriage has been approved. But churches continue either to be convulsed by this question or to choose not to address it. Let me lead you through a rapid tour which may help to explain why this is.

Secular societies such as Scotland tend also to be relatively open, permissive and to some extent liberal. Change therefore can happen quickly. Churches by contrast have their roots deep down in history and tradition. Sacred texts and time-hallowed ways of understanding the sacredness of life and its meaning make rapid movement very difficult. Are we simply accommodating ourselves to societal change at the risk of becoming detached from our tradition of faith?

Within churches, human sexuality issues have the capacity to expose deep fault lines in our understanding of faith. Some see the full inclusion of LGBT people as a matter of justice. Jesus was a person always open to those excluded by others – the lepers, the adulterous woman, tax collector and sinners. Would he not have been also open to LGBT people? Others point to the authority of scripture which in some places warns against same sex relationships. They call us to an understanding of God's law and life as it has been understood from the creation.

So this is an important moment for our church. It is not just about whether we can find agreement, it is about whether what we do is within our understanding of our faith.

The Most Rev David Chillingworth, Bishop of St Andrews,Dunkled & Dunblane and Primus of the Scottish Episcopal Church