Finally then, brothers, we beg and exhort you in the Lord Jesus, that as you received from us how you ought to walk and to please God, that you abound more and more.
In the Lord Jesus ...  This is Paul's great phrase used so frequently in his writings (169 times) to indicate the status of believers in relationship to Christ.  Here the thought is that all of his instructions have been conveyed to them in respect of their common bond "in Christ," and in view of his apostolic relationship to the Lord himself.