The category which he names next is not composed of different persons from the first, but of the same persons regarded from a somewhat different point of view. 'Them that are under the law' describes Jews, not by their race, but by their religion; and Paul was willing to take his place among them, as we have just observed. But he will not do that so as to be misunderstood, wherefore he protests that in doing so he is voluntarily abridging his freedom for a specific purpose. He is not 'under the law'; for the very pith of his view of the Christian's position is that he has nothing to do with that Mosaic law in any of its parts, because Christ has made him free.
The second class to whom in his wide sympathies he is able to assimilate himself, is the opposite of the former--the Gentiles who are 'without law.' He did not preach on Mars' Hill as he did in the synagogues. The many-sided Gospel had aspects fitted for the Gentiles who had never heard of Moses, and the many-sided Apostle had links of likeness to the Greek and the barbarian. But here, too, his assimilation of himself to those whom he seeks to win is voluntary; wherefore he protests that he is not without law, though he recognises no longer the obligations of Moses' law, for he is 'under [or, rather, "in"] law to Christ.'
'The weak' are those too scrupulous-conscienced Christians of whom he has been speaking in chapter viii. and whose narrow views he exhorted stronger brethren to respect, and to refrain from doing what they could do without harming their own consciences, lest by doing it they should induce a brother to do the same, whose conscience would prick him for it. That is a lesson needed to-day as much as, or more than, in Paul's time, for the widely different degrees of culture and diversities of condition, training, and associations among Christians now necessarily result in very diverse views of Christian conduct in many matters. The grand principle laid down here should guide us all, both in regard to fellow-Christians and others. Make yourself as like them as you honestly can; restrict yourself of allowable acts, in deference to even narrow prejudices; but let the motive of your assimilating yourself to others be clearly their highest good, that you may 'gain' them, not for yourself but for your Master.
Verse 23 lays down Paul's ruling principle, which both impelled him to become all things to all men, with a view to their salvation, as he has been saying, and urged him to effort and self-discipline, with a view to his own, as he goes on to say. 'For the Gospel's sake' seems to point backward; 'that I may be a joint partaker thereof points forward. We have not only to preach the Gospel to others, but to live on it and be saved by it ourselves.