The question of secession from fellowship, later in 1 John 2, deserves a separate post. Here its the first part of 1 John 2 to which attention is paid.
'we have come to know him (Jesus Christ), if we keep his commandments' (v. 3).
There can be no fellowship or communion with Jesus Christ when we do not keep his commandments. This sets up some tension in the teaching of 1 John: what if we do not keep his commandments, that is, what if we sin? Has fellowship irreparably ended?
Intriguingly John offers not only assurance that sins are forgiven (1:7-2:2) but also acknowledges two levels of disobedience (5:16-17) while being clear that 'all wrongdoing is sin'. Yet, logically consistent with the connection he makes between fellowship and obedience, the author knows that a Christian person cannot keep on sinning (3:6; 5:18). One question of 1 John is whether, in the end, it satisfactorily resolves the tension between sin/confession/forgiveness and not continuing to sin. (If it does not resolve the tension that is no reason to ignore 1 John - it exists for us within the whole canon of Scripture and the more important question is the resolution of such issues by the whole of Scripture).
Moving right along from that difficult question (!!), and back to the Anglican Communion, 1 John supports the general case of conservative Anglicans that (a) sin is a significant issue in the life of the believer and of the church (b) sin is an issue for 'fellowship' or 'communion', and not just in terms of (say) unbalancing the moral equilibrium of the universe (c) sin is not only a general state of human fallibility but also concerns specific commandments which we either keep or do not keep.
Yet there is a further difficult question lurking in 1 John 2 and that is the question of what the commandments are with which we should be concerned about our keeping them or not. I shall post on that soon.