1 John 2:3

And hereby we know that we know him, if we keep his commandments.

Contrary to the criterion accepted by many for determination if they are or are not saved, this denies that a person's "feelings" in such a question can be trusted. "It is all too easy to fall into illusions about ourselves if we make too much of our religious feelings, even those of an elevated kind."[12] Keeping the commandments of God is the prerequisite and the test either of loving God (John 14:15) or of knowing God. Macknight supposed that John here was teaching against "the Nicolaitans and Gnostics who affirmed that the only thing necessary to eternal life was the knowledge of the true God."[13]

Hereby we know ... Similar words are used several times in this letter to introduce "tests" by which the validity of one's faith might be tested (1 John 2:5,29; 1 John 3:19,24; 1 John 4:2,6,13, and 1 John 5:2). In the last analysis, it is keeping the commandments of the Lord, walking in the light, doing the truth, obeying the word, etc., which are the final determinator of whether one is saved or lost. Which commandments are meant? All of them. There is no way to limit these to the ethical or moral commandments; those relating to the worship of God are likewise included. To keep God's commandments is equivalent to keeping his word, "And this means the truth of God as it is in Christ."[14] The obligation extends to the entirety of the New Testament revelation.

[12] Amos N. Wilder, The Interpreter's Bible, Vol. XII (New York: Abingdon Press, 1957), p. 226.

[13] James Macknight, op. cit., p. 41.

[14] Harvey J. S. Blaney, op. cit., p. 363.