How are they no longer in the world? By no longer participating in the temporal common good, but wholly serving the supernatural common good in itself. Religious are no longer are bound by duties to family or their native political communities, etc. Their ties to family and community are severed. This does not mean that they do not have relations with a political community -- they may maintain economic relations. For example, even a self-sustaining monastery may exchange goods with members of the local community. The mendicants and members of younger religious orders created during and after the Catholic Reformation are primarily dependent upon the surplus wealth of the lay faithful. In that respect, only a few have been privileged to depend on God alone for their survival.
Would the apostolic works of the mendicants and active religious be considered a part of the temporal common good, or only a part of the supernatural common good? It seems that it would be the latter, if we understand the temporal common good to be obtainable by our power alone. If the temporal common good were identified with the complete perfection of the community, then one would have to take grace and supernatural perfection into account, but this is not something which man holding temporal authority (and nothing more) can provide, only God through His Church.
Is a temporal authority, then, concerned with natural perfection alone? Is there anything here that would preclude the hierarchy of the Church from wielding temporal authority in a Christian polity? Temporal authority is subject to the supernatural authority of the Church, but can the latter not hold both, just as charity is a general virtue which commands the other virtues? (Would it be the case then that temporal authority can be permitted to be separate, or that it can be delegated by the Church to others?)
Before Christ, temporal authority was limited in what it could bring about. With the Incarnation, has it been superceded by the authority of the Church with respect to Christian polities (or absolutely, with respect to all polities)?
A bottom-to-top approach in understanding the political community might lead one to think that a temporal authority must be separate from the supernatural authority of the Church, which, as the superior power, is placed over the temporal authority or recognized by the temporal authority as such.
To answer these questions we might have to reconsider what the end of living in common is: to provide for the perfection of all members through work and mutual exchange but also to live with others for its own sake... De Regno discusses why political authority is necessary -- because the common good is not identical to the private good of its members.
The supernatural common good is God; the hierarchy of the Church does legislate as to how charity is to be exercised. (To a limited extent? The bishops are more guides, pastors, than rulers of the Church?)
Is the political common good subsumed or incorporated into the supernatural common good, or is it kept separate but subordinate? Is it necessary to keep the political common good separate because in a polity there are sinners living with the just, and the laws of a polity must be proportioned to its members accordingly? (Humans are competent to judge only sensible actions. Hence this is one reason why the Church's authority with regard to the supernatural common good is limited?)
Social life does not require as much as living in union with God, and so laws which maintain external peace between the members of a community and command acts of justice can be imposed on both sinners and the just. The laws for a political community are therefore distinct from those for the supernatural community, the Church. But this does not necessitate that a bishop may not hold temporal authority. (Although it may be prudent for him not to, since his function is to take care of the Church and concern for temporal affairs may take away too much time, etc. from his pastoral work.) One could also argue that there should be a division of power in order to prevent an abuse of power.
