The whole of the gospel needed for the salvation of our souls has been given. And therefore, anything which adds to that gospel or anything which takes away from that gospel—be it a new truth or a new morality, other than that which the gospel itself endorses—any additions to the gospel or any deletions from the gospel, against those we must earnestly contend because God delivered it complete unto us. It was once for all delivered unto the saints. Thus, if we allow for an addition to the Word of God, a deletion from the Word of God, or a substitution of man's morality rather than the clearly revealed biblical reality, then we deny the faith.1
John McKnight
3 Beloved, although I was very eager to write to you about our common salvation, I found it necessary to write appealing to you to contend for the faith that was once for all delivered to the saints.