A few threads that might orient you:
Conditional Election - Where does FV differ from Historical Reformed Usage? Wilkins' Presbytery exam examined by Rick Phillips
In a nutshell, the Scriptural position is that union with Christ is laid hold of by Evangelical faith. That is, it is born from above.
While the entire Congregation is preached to with the same promises and the same sort of injunctions, not all participate in mystical union with Christ simply by being a member of the Church.
There are several errors but chief among them is the idea that, when one is baptized into the Church, all are united to Christ and have the benefits of that union with Christ in some sense: all are in
some sense forgiven of their sins, have peace with God, etc. The manner in which that status is maintained is by faithfulness to the Covenant so that, in the last day, those that are finally justified are those that did not forsake Covenant membership.
I'm certain there are those that will take issue with the basic explanation but the bottom line is that our union with Christ is not simply by being
visibly joined to the Covenant of Grace. Baptism does not unite us to Christ. Faith does. Those that do not have faith that is born from above are in no sense forgiven of their sins. Do they hear the preaching of God and taste the heavenly gift? Are all members preached to with the expectation that all should fear lest any be found to be unbelieving?
Yes and yes. But none are justified in some sense. It is only those that have been elect from the foundation of the world, that have been regenerated by the Gospel, and have been given Evangelical faith that are united to Christ in His death and resurrection. The fact that the congregation is preached to with the expectation that all must respond in a way that only the elect truly can does not, in turn, imply that all are able to do so
in some sense.