Dearly loved ones, as I was very eagerly planning to write to you about the salvation we share in common, I felt it necessary [instead] to write urging you to contend earnestly for the faith [i.e., the teaching of Christ] which was once and for all delivered [by the apostles, See verse 17] to the saints [i.e., God's holy people].

But these people [i.e., the "certain men" of verse 4] speak against whatever they do not understand, and what they do understand naturally, the way animals do, proves to be their ruination.