Everyone who sins also commits lawlessness. Sin is lawlessness.
It seems evident that the apostle is here combating an opinion which then existed that people might sin, and yet be true Christians, 1 John 3:7; and he apprehended that there was danger that this opinion would become prevalent. On what ground this opinion was held is unknown. Perhaps it was held that all that was necessary to constitute religion was to embrace the doctrines of Christianity, or to be orthodox in the faith; perhaps that it was not expected that people would become holy in this life, and therefore they might indulge in acts of sin; perhaps that Christ came to modify and relax the law, and that the freedoM which he procured for them was freedom to indulge in whatever people chose; perhaps that, since Christians were heirs of all things, they had a right to enjoy all things; perhaps that the passions of people were so strong that they could not be restrained, and that therefore it was not wrong to give indulgence to the propensities with which our Creator has formed us. All these opinions have been held under various forms of Antinomianism, and it is not at all improbable that some or all of them prevailed in the time of John. The argument which he urges would be applicable to any of them. The consideration which he here states is, that all sin is a transgression of law, and that he who commits it, under whatever pretence, is to be held as a transgressor of the law. The literal rendering of this passage is, “He who doeth sin (ἁμαρτίαν hamartian ) doeth also transgression” - ἀνομίαν anomian. Sin is the generic term embracing all that would be wrong. The word transgression (ἀνομία anomia) is a specific term, showing where the wrong lay, to wit, in violating the law.