Ever since the Middle Ages there has been disagreement between Christians who expect changes and those who expect the Church to stay the same.
Today we usually think of history in linear terms: there was a beginning a long time ago, human societies have changed over time and will continue to change in the future. We do not expect our great-grandchildren to have the same lifestyles as we have. We have inherited this linear conception of history largely from the Old Testament prophets.
In ancient and medieval times history was often conceived differently. Either it went round in circles, or it alternated between a golden age and a dark age, or there was a succession of ages. Most medieval Christians thought in terms of ages: from the Creation to the Fall, from the Fall to the time of Christ, and the current age from the time of Christ to the Second Coming.
Although Christians today are familiar with this concept, we rarely apply its logic because we also accept the linear view (despite the contradictions between the two). Most medievals believed that within each age life carried on pretty well exactly the same. They therefore believed that their own lifestyles were virtually identical to the lifestyles of the early Christians.
This was the context of the Reformation debates, where Catholics and Protestants alike accused each other of innovating, while claiming that their own church was exactly the same as the New Testament Church. The logic of these positions was that the Church ought not to change at all. Both the Council of Trent and the foundational documents of sixteenth century Protestant churches were heavily influenced by this conception.
Some of the Renaissance humananists had already raised awareness of gradual historical development, and this was revived towards the end of the seventeenth century with the Enlightenment. Anglicans, following the sixteenth century Richard Hooker, affirmed his claim that there is a proper place for development: the church 'has authority to establish that for an order at one time, which at another it may abolish, and in both do well'.
Attitudes to development are closely related to beliefs about revelation. If we think there is a single supreme authority like the Bible which lays down for all time the truths and moral rules of Christianity, it is harder to justify new developments. If, on the other hand, we have a variety of authorities, including new insights and experiences, and see it as our task to balance them against each other, new developments over time are not only defensible but to be expected. Thus Hooker's account of 'scripture, reason and tradition' makes it easier to justify development. Some add 'experience'. Scripture and tradition root us in the past while reason and experience help us seek God's will as we respond to new situations.
Nobody today expects an unchanging world the way our sixteenth century ancestors did; we are only too aware of the vast range of new technologies. However, many religious conservatives have inherited the idea in a weakened form, so that regardless of what happens in the secular world, the Church should not change. This idea is currently being expressed in the debates about same-sex partnerships and women priests and bishops, though at every stage of church history there have always been changes, and controversies about changes.
The Anglican Covenant, while not rejecting all changes, presents them as potential problems and emphatically gives the benefit of the doubt to opponents. Instead of affirming the traditional Anglican authorities of scripture, reason and tradition, let alone experience, it expects each church 'to seek a shared mind with other Churches, through the Communion's councils, about matters of common concern, in a way consistent with the Scriptures, the common standards of faith, and the canon laws of our churches' (3.2.4). Thus every decision would have to refer back to the Bible and canon law, leaving no room for new insights.
This is deliberate. The Covenant is designed to forbid developments like the recent North American ones. If they had included reason and experience in the list of permitted authorities, they would not have been able to condemn them as contrary to Anglican teaching.