Jamieson, Fausset and Brown on 2 Peter 1:2

2. Grace ... peace--(1Pe 1:2).

through--Greek, "in": the sphere IN which alone grace and peace can be multiplied.

knowledge--Greek, "full knowledge."

of God, and of Jesus our Lord--The Father is here meant by "God," but the Son in 2Pe 1:1: marking how entirely one the Father and Son are (Joh 14:7-11). The Vulgate omits "of God and"; but oldest manuscripts support the words. Still the prominent object of Peter's exhortation is "the knowledge of Jesus our Lord" (a phrase only in Ro 4:24), and, only secondarily, of the Father through Him (2Pe 1:8; 2Pe 2:20; 3:18).