NOTES for Co2 6:11-18
Continuing the discussion of the Kingdom and the life of the Kingdom, Paul again reminds the Corinthian brothers that spiritual life requires definiteness of choice and an unambiguous spiritual and moral assessment of both righteous and sinful human actions (vv. 14-18). These words clearly echo the Savior's own words about the impossibility of serving two masters, words that in turn summed up the teaching, traditional for Yahwism and Judaism, about the two ways: the way of sin and the way of righteousness.
But Paul does not confine himself merely to reminding them of things the Corinthian Christians should have known no worse than he did. For him, the main problem becomes not a moral problem as such, but a spiritual one. Here too, however, Paul follows the tradition: from the point of view of the Torah, the most terrible thing about sin is not that it is immoral, but that it separates the sinner from God, raising a wall between them that cannot be destroyed without repentance and renewed turning back. The apostle, as we can see, shifts the emphasis from the relationship between a person and God to the relationship between inhabitants of the Kingdom, though those relationships can hardly be considered apart from their relationship with God.
He tells his Corinthian brothers that because of the sins they commit he finds himself cramped in their hearts, while his own heart and the hearts of his companions are widened so that there is no narrowness in them (vv. 11-12). But, the apostle adds, "as to children, a corresponding recompense will be extended to you" (v. 13), so that those whose hearts are narrow will not be able to experience the breadth of heart they might otherwise find in Paul. Even after becoming an inhabitant of the Kingdom, a person subject to the action of the evil in which our still untransformed world remains until the Savior returns receives into his heart only that measure of the life of the Kingdom that is determined by his resolve to resist that evil. Then a person's indecision on the spiritual path, the attempt to serve two masters, not only deprives him of the fullness of the life of the Kingdom, but also deprives others of the possibility of full communion with such an indecisive Christian.
That is why Paul feels cramped in the hearts of some of his Corinthian brothers. And he tells them this directly, perhaps wishing to remind them of the time when nothing hindered their spiritual unity. A time when they no doubt breathed in the breath of the Kingdom with full lungs, as Christians should.