even denying the Lord that bought them] The word for Lord (despotes), literally, a master as contrasted with a slave (1Ti_6:1-2), is used of Christ here, in the hymn, which we may fairly connect with St Peter, in Act_4:24, in Rev_6:10, and, in conjunction with the more common word for Lord (Kyrios), in Jdg_1:4. Here the choice of the word was probably determined by the connexion with the idea of “buying,” as a master buys a slave. The use of that word presents a parallelism with the thought of 1Pe_1:18, and here, as there, we have to think of the “precious blood of Christ” as the price that had been paid. No words could better assert the truth that the redemption so wrought was universal in its range than these. The sin of the teachers of these “heresies of perdition” was that they would not accept the position of redeemed creatures which of right belonged to them. The “denial” referred to may refer either to a formal rejection of Christ as the Son of God, like that of 1Jn_2:22-23, or to the practical denial of base and ungodly lives. The former is, perhaps, more prominently in view, but both are probably included. We cannot read the words without recollecting that the writer had himself, in one memorable instance, denied his Lord (Mat_26:69-75). In his case, however, the denial came from a passing cowardice and was followed by an immediate repentance. That which he here condemns was more persistent and malignant in its nature, and was as yet unrepented of.
Cambridge Commentary