He that saith, he abideth in him - Greek, “remains” in him; that is, abides or remains in the belief of his doctrines, and in the comfort and practice of religion. The expression is one of those which refer to the intimate union between Christ and his people. A great variety of phrase is employed to denote that. For the meaning of this word in John, see the notes at 1 John 3:6.
Ought himself also so to walk, even as he walked - Ought to live and act as he did. If he is one with him, or professes to be united to him, he ought to imitate him in all things. Compare John 13:15. See also the notes at 1 John 1:6.