"who privily shall bring in damnable heresies: errors in the fundamental doctrines of the Gospel; such as relate to a trinity of persons in the Godhead; and to the person of Christ, to his proper deity, distinct personality, eternal sonship, and real humanity; and to his office as Mediator, rejecting him as the true Messiah, and as the only Saviour of sinners; denying his sacrifice and satisfaction, and the imputation of his righteousness; and to the Holy Spirit, his deity, personality, and divine influences and operations: these are "damnable", or "destructive", or "heresies of destruction"; which lead to eternal destruction both those that introduce and propagate them, and those that embrace and profess them; for they remove, or attempt to remove, the foundation of eternal life and happiness: the manner in which these are usually introduced is "privily"; at unawares, secretly, under a disguise, and gradually, by little and little, and not at once, and openly; and which is the constant character and practice of such men, who lie in wait to deceive, creep into churches...unawares, and into houses privately; and insinuate their principles under specious pretences and appearances of truth, using the hidden things of dishonesty, walking in craftiness, handling the word of God deceitfully, and colouring things with false glosses and feigned words: and even denying the Lord that bought them; not the Lord Jesus Christ, but God the Father; for the word κυριος is not here used, which always is where Christ is spoken of as the Lord, but δεσποτης; and which is expressive of the power which masters have over their servants, and which God has over all mankind; and wherever this word is elsewhere used, it is spoken of God the Father, whenever applied to a divine person, as in Luke 2:29 and especially this appears to be the sense, from the parallel text in Jude 1:4 where the Lord God denied by those men is manifestly distinguished from our Lord Jesus Christ, and by whom these persons are said to be bought: the meaning is not that they were redeemed by the blood of Christ, for Christ is not intended; and besides, whenever redemption by Christ is spoken of, the price is usually mentioned, or some circumstance or another which fully determines the sense; see Acts 20:28 whereas here is not the least hint of anything of this kind: add to this, that such who are redeemed by Christ are the elect of God only, the people of Christ, his sheep and friends, and church, and who are never left to deny him so as to perish eternally; for could such be lost, or deceive, or be deceived finally and totally by damnable heresies, and bring on themselves swift destruction, Christ's purchase would be in vain, and the ransom price be paid for nought; but the word "bought" regards temporal mercies and deliverance, which these men enjoyed, and is used as an aggravation of their sin in denying the Lord; both by words, delivering out such tenets as are derogatory to the glory of the divine perfections, and which deny one or other of them, and of his purposes, providence, promises, and truths; and by works, turning the doctrine of the grace of God into lasciviousness, being disobedient and reprobate to every good work; that they should act this part against the Lord who had made them, and upheld them in their beings and took care of them in his providence, and had followed them with goodness and mercy all the days of their lives."
- excerpt from John Gill's Bible commentary on 2 Peter 2:1