Ephesians 2:8-9 For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: Not of works, lest any man should boast.
Romans 6:14 For sin shall not have dominion over you: for ye are not under the law, but under grace.
Jude 4 For there are certain men crept in unawares, who were before of old ordained to this condemnation, ungodly men, turning the grace of our God into lasciviousness, and denying the only Lord God, and our Lord Jesus Christ.
… intimating that men might sin safely who believe the Gospel, because in that Gospel grace abounds.
Turning the grace of our God into lasciviousness – Abusing the doctrines of grace so as to give indulgence to corrupt and carnal propensities.
That is, probably, they gave this form to their teaching, as Antinomians have often done, that by the gospel they were released from the obligations of the law, and might give indulgence to their sinful passions in order that grace might abound. Antinomianism began early in the world, and has always had a wide prevalence.
The liability of the doctrines of grace to be thus abused was foreseen by Paul, and against such abuse he earnestly sought to guard the Christians of his time, …(Romans 6:1 What shall we say then? Shall we continue in sin, that grace may abound?)
And denying the only Lord God, and our Saviour Jesus Christ –
That is, the doctrines which they held were in fact a denial of the only true God, and of the Redeemer of men.
2 Peter 2:1 But there were false prophets also among the people, even as there shall be false teachers among you, who privily shall bring in damnable heresies, even denying the Lord that bought them, and bring upon themselves swift destruction.
It cannot be supposed that they openly and formally did this, for then they could have made no pretensions to the name Christian, or even to religion of any kind; but the meaning must be, that “in fact” the doctrines which they held amounted to a denial of the true God, and of the Saviour in his proper nature and work.
Their doctrines and practice tended as really to the denial of the true God as they did to the denial of the Lord Jesus.
Peter, in 2 Peter 2:1, has adverted only to one aspect of their doctrine – that it denied the Saviour; Jude adds, if the common reading be correct, that it tended also to a denial of the true God.
… that their doctrines amounted to a practical denial of the only true God; and equally so that they were a denial of the only Sovereign and Lord of the true Christian.