2 John 3 (ESV) … “Grace, mercy, and peace will be with us, from God the Father and from Jesus Christ the Father’s Son, in truth and love.”
This is guaranteed: “Grace be with you, mercy, and peace, from God the Father, and from the Lord Jesus Christ, the Son of the Father, in truth and love” (v. 3). Grace, peace, mercy—that’s what Satan is up against when he attacks a believer. He may win some tactical battles, but he cannot win the war. Grace means that the limitless resources of God’s lovingkindness and tender mercy have been harnessed on the believer’s behalf. God’s unmerited and unbounded favor cuts all the ground from beneath the Enemy’s feet. Peace means the war is over; it has already been won. As a result of Calvary, Satan’s activities are severely restricted (Col. 2:14–15). He can act only by divine permission and under divine supervision and in accordance with the mystery of God’s permissive will. Mercy means that God will not allow Satan to go any further against us than we are able to bear and that, in each case, a way of escape is provided for us (1 Cor. 10:13).
All this is assured by God the Father and God the Son. John here deliberately equates the Son with the Father as coequal, coexistent, and coeternal. Satan, for all his diligence and resourcefulness, is on the losing side.
 Phillips, J. (2009). Exploring the Epistles of John: An Expository Commentary (2 Jn 3). Kregel Publications; WORDsearch Corp.