Let no man seek his own (mēdeis to heautou zēteitō). This is Paul’s rule for social relations (1Co 13:5; Gal 6:2; Rom 14:7; Rom 15:2; Phi 2:1.) and is the way to do what is expedient and what builds up.
His neighbour’s good (to tou heterou). Literally, “the affair of the other man.” Cf. ton heteron in Rom 13:8 for this idea of heteros like ho plēsion (the nigh man, the neighbour) in Rom 15:2. This is loving your neighbour as yourself by preferring your neighbour’s welfare to your own (Phi 2:4).