The Church of England is a parochial church. Whatever some ecclesiologists may say the heart of the Church of England, both legally and I believe effectively, lies in its parishes. The law is based far more on Churchwardens and PCCs than on diocesan boards or indeed bishops. Incumbents have very specific legal rights meant to ensure their independence of bishops, patrons and PCCs. This rightly preserves the duty of the incumbent to follow his or her conscience within the parameters of Canon Law and the Measures which spring from that. I know that Common Tenure is sometimes seen as challenging that, and most of us want to be paid, so there is a necessary relationship with the Diocesan Board of Finance, but both parish and incumbent retain their own rights and duties which are not subject to episcopal, diocesan or even archidiaconal behest.
So I believe that a diocese is the servant of parochial mission. The parish is responsible to and for its local community, so that there is a duty to take up the Christian care of everyone, and the proclaiming of the good news of Jesus Christ to everyone.
Nevertheless the diocese is more than a group of parishes who have got together for mutual support or defence.