1 John 2:4

He that saith. Compare on ch. 1:6. It is probable that there were those who, influenced by such heresies as Docetism (see p. 625), actually claimed to know Christ while disregarding His commandments. It is to such persons that John obliquely refers to avoid naming them or specifically including his readers among their number (cf. ch. 2:6, 9). There was no excuse for these deceptive teachings in the church, for Christ had emphatically declared that he who is willing to receive truth will have it revealed to him (see on John 7:17), and that those who truly love Him will keep His commandments (see on ch. 14:15).

Is a liar. Such a person’s character, as well as his profession, is false; by these he proves that “the faith is not in him” (cf. on ch. 1:6, 8). Note again the use of both the positive and negative expressions (cf. ch. 1:5, 6, 8, 10).