NOTES for Rom 11:25
The apostle is fully convinced that Christ's coming and the beginning of the era of the new, messianic covenant in no way devalues the path that was traveled by the people of God in pre-Christian times, and by no means closes to Jews the possibility of entering the Kingdom and the Church later. At the same time Paul says that first the Church must be filled out by converts from the pagans, must increase in number. And the point here is not that pagans can become some kind of example for Jews or convince them of something by their mass conversion to Christ, even if such mass conversion were possible.
The point is that only the fullness of the Church, manifested to the world, can be truly convincing for those who have traveled a certain part of the way into the Kingdom and stopped in the confidence that they have already reached the goal. The issue is, of course, precisely the fullness of the whole Church. A Church not reducible to any communal movements, still less to any earthly structures and institutions, but representing the form of the Kingdom's existence on earth and the space of relations uniting the faithful with Christ. Sometimes such a Church is called heavenly, sometimes mystical, and neither definition can be considered complete.
The fullness of the Church includes not only heaven but also earth, not only those who have already completed the earthly stage of their Christian path but also those who are still continuing it. And fullness in one part of the Church, provided there is full Christian life, is manifested no less than in another, though in a different form. Nor, in essence, is there so very much mysticism in church life: it is proper to a divided world, when inhabitants of one part of it try to peer into another to which they have no access.
But the Church, the true Church and not the human institutions stuck to it, is always open in every sense; there is mystery in it, but no mysteriousness or esotericism so loved by many mystics. This true Church in all its fullness can become for those who have stopped on the way into the Kingdom a stimulus for further movement. Everything else is usually unconvincing for such people. Paul knows this from his own experience.