He that saith he abideth in him As he has before set before us God as light for an example, he now calls us also to Christ, that we may imitate him. Yet he does not simply exhort us to imitate Christ; but from the union we have with him, he proves that we ought to be like him. A likeness in life and deeds, he says, will prove that we abide in Christ. But from these words he passes on to the next clause, which he immediately adds respecting love to the brethren.

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.

Abideth in him - He who not only professes to have known Christ, but also that he has communion with him, and abides in his favor, should prove the truth of his profession by walking as Christ walked; living a life of devotion and obedience to God, and of benevolence and beneficence to his neighbor. Thus Christ walked; and he has left us an example that we should follow his steps.
To be in Christ, 1-John 2:5, is to be converted to the Christian faith, and to have received the remission of sins. To abide in Christ, 1-John 2:6, is to continue in that state of salvation, growing in grace, and in the knowledge of our Lord Jesus Christ.

(5) He that saith he abideth in him ought himself also so to walk, even as he walked.
(5) He that is one with Christ, must live his life, that is, must walk in his steps.

He that saith he abideth in him,.... As all do that are in him; once in Christ, and always in Christ; they are set as a seal on his arm and heart, which can never be removed; they are in his arms, and can never be plucked from thence; and are members of him, and can never be disunited from him: or dwelleth in him, as in John 6:56; that is, by faith; who under a sense of sin and danger have fled to Christ, as to a strong tower and place of defence, where they dwell safely, peaceably, pleasantly, and comfortably, enjoying whatever is necessary for them. The Syriac and Ethiopic versions read, "he that saith I am in him"; loved by him, chosen in him, united to him, a member of his, and have communion with him:
ought himself also to walk even as he walked; as Christ walked, lived, and acted, so ought he; that is, to imitate him and follow him, as he has him for an example; not in his miraculous works in raising the dead, healing the sick, and walking upon the waters, &c. which were wrought as proofs of his deity and of his Messiahship, and not intended for imitation; nor in his mediatorial performances, as in his propitiatory sacrifice and advocacy; but in the exercise of grace, and duties of religion as a man, and in a private way; and may chiefly regard walking in love, as he walked, see Ephesians 5:2; and is what is in the following verses insisted on, namely, the new commandment of love to the brethren; which should be to all as his was, and, like his, constant and lasting; and, when the case requires, should be shown by laying down life for them. The "as" is not a note of equality, but of likeness; for it cannot be thought that saints should walk in that degree of perfection, in humility, patience, love, and in the exercise of every other grace, and in the discharge of duty, as Christ did; only that they should copy after him, and make his obedience and life the rule of theirs.

abideth--implying a condition lasting, without intermission, and without end.
He that saith . . . ought--so that his deeds may be consistent with his words.
even as he--Believers readily supply the name, their hearts being full of Him (compare John 20:15). "Even as He walked" when on earth, especially in respect to love. John delights in referring to Christ as the model man, with the words, "Even as He," &c. "It is not Christ's walking on the sea, but His ordinary walk, that we are called on to imitate" [LUTHER].

He that saith he abideth in him - which implies a durable state; a constant, lasting knowledge of, and communion with, him. Ought himself - Otherwise they are vain words. So to walk, even as he walked - In the world. As he, are words that frequently occur in this epistle. Believers having their hearts full of him, easily supply his name.