For if we sin wilfully,....] Which is not to be understood of a single act of sin, but rather of a course of sinning; nor of sins of infirmity through temptation, or even of grosser acts of sin, but of voluntary ones; and not of all voluntary ones, or in which the will is engaged and concerned, but of such which are done on set purpose, resolutely and obstinately; and not of immoral practices, but of corrupt principles, and acting according to them; it intends a total apostasy from the truth, against light and evidence, joined with obstinacy.
After that we have received the knowledge of the truth; either of Jesus Christ, or of the Scriptures, or of the Gospel, or of some particular doctrine, especially the principal one, salvation by Christ; of which there may be a notional knowledge, when there is no experimental knowledge; and which is received not into the heart, but into the head: and whereas the apostle speaks in the first person plural, we, this is used not so much with regard to himself, but others; that so what he delivered might come with greater weight upon them, and be more readily received by them; when they observed he entertained no hard thoughts or jealousies of them, which would greatly distress the minds of those that were truly gracious.
Moreover, the apostles use this way of speaking, when they do not design themselves at all, but others, under the same visible profession of religion, and who belonged to the same community of believers; see 1Pe 4:3 compared with Ac 22:3.
Besides, these words are only hypothetical, and do not prove that true believers could, or should, or do sin in this manner: to which may be added, that true believers are manifestly distinguished from these persons, Heb 10:38,there remaineth no more sacrifice for sins; meaning, not typical sacrifice; for though the daily sacrifice ought to have ceased at the death of Christ, yet it did not in fact until the destruction of Jerusalem; but the sacrifice of Christ, which will never be repeated; Christ will die no more; his blood will not be shed again, nor his sacrifice reiterated; nor will any other sacrifice be offered; there will be no other Saviour; there is no salvation in any other, nor any other name whereby we must be saved.