Georg Vicedom, in his classic work, The Mission of God: An Introduction to a Theology of Mission writes,
Hence God Himself does mission work. In His mercy He once more makes Himself the Shepherd and Messenger of His people languishing in confusion (Matthew 9:36; Mark 6:34). He sends the Servant of God, from whose promises the Old Testament church of God has learned that its God is a God of the nations. He does His mission work through His Son, who Himself becomes an apostle, that is, one who is sent (Heb. 3:1). In Him He makes the salvation intended for all men a reality and calls them anew into His fellowship.
The special missio Dei begins with Jesus Christ, for in Him God is both the Sender and the One who is sent, both the Revealer and the Revelation, both the Holy One who punishes and the One who redeems. Through His Son in the incarnation and enthronement God makes Himself the very content of the sending. Through His Son it becomes clear once and for all who God is, what He is, how He works, how He thinks in regard to men, how He redeems them, what salvation He has prepared for them, how men may draw nigh unto Him, and how they are received into His fellowship. That now applies to all men. No one can seek his own way of salvation. No one can sidestep this Jesus. Everyone must decide about Him and through Him, for in Him the God who is their Lord since creation deals with men.
From: The Mission of God: An Introduction to a Theology of Mission by Georg Vicedom. Translated by Gilbert A Thiele and Dennis Hilgendorf. St. Louis: Concordia Publishing House, 1987, p. 52.