Rejoice with them that do rejoice, and weep with them that weep.
Note 9 at Ro 12:15: Self-centered people will not rejoice at someone else's prosperity. They will be jealous instead. Likewise, selfish people will not weep with those that weep, because they really don't care about anyone but themselves. Paul was continuing the thought about preferring one another (see note 4 at Ro 12:10).