ectypal.net

...this relation between Father and Son, though most clearly manifest during Christ’s sojourn on earth, was not first initiated at the time of the incarnation, for the incarnation itself is already included in the execution of the work assigned to the Son, but occurs in eternity and therefore also existed already during the time of the Old Testament. Scripture also clearly attests this fact when it attributes the leadership of Israel to the Angel of Yahweh (Exod. 3:2f.; 13:21; 14:19; 23:20-23; 32:34; 33:2; Num. 20:16; Isa. 63:8-9), and sees Christ also functioning officially already in the days of the Old Testament (John 8:56; 1 Cor. 10:4, 9; 1 Pet. 1:11; 3:19). For there is but one mediator between God and humankind (John 14:6; Acts 4:12; 1 Tim. 2:5), who is the same yesterday and today and forever (Heb. 13:8), who was chosen as Mediator from eternity (Isa. 42:1; 43:10; Matt. 12:18; Luke 24:26; Acts 2:23; 4:28; 1 Pet. 1:20; Rev. 13:8), and as Logos existed from eternity as well (John 1:1, 3; 8:58; Rom. 8:3; 2 Cor. 8:9; Gal. 4:4; Phil. 2:6; etc.).