A standard Greco-Roman letter opened with (1) the author, (2) the recipients, and (3) a grace-wish. The letters of the New Testament are remarkable in how they expand upon these expected elements, especially the third part of the greeting.
Jude’s grace-wish in v. 2 of his letter is short and to the point:
May mercy, peace, and love be multiplied to you
A few observations:
(1) Jude uses another triplet (mercy, peace, and love), his second so far in the letter (see v. 1b for the triplet of called, beloved, and kept).
(2) This is a prayer for something to happen (“May…be multiplied to you”), something Jude knows God alone can grant.
(3) Where you might expect the word “grace” Jude uses “mercy.” The greetings in 1 Timothy, 2 Timothy, and 2 John include “mercy” after “grace,” but Jude doesn’t mention “grace” in v. 2 at all. Most New Testament letters just have “grace and peace,” which means Jude deviates from this pattern.
Now why the terms “mercy, peace, and love”? Each term appears to be chosen in light of concerns raised later in the letter, for concepts in letter-greetings are often worked out in subsequent arguments. The three words, then, foreshadow what’s coming.
Jude will tell his readers to “have mercy on those who doubt” (v. 22), so they need God’s blessing of mercy among them in order to obey that command. “Peace” is important for the recipients because the intruders are scoffers rejecting authority and causing division (vv. 8, 18-19). And “love” will be necessary in order to sufficiently contrast with the unloving and selfish actions of the intruders who care only for themselves (v. 12). Jude’s readers must keep themselves in God’s love (v. 21).
In addition to the polemical importance of Jude’s triplet in v. 2, some scholars suggest a designed order of mercy, then peace, then love. Since the triad can easily be connected to the good news of the gospel, perhaps Jude has in mind saving mercy that results in peace with God and bears the fruit of love.
Jude 2 appears to be significant, then, for two reasons: (1) the triplet plants words that Jude will soon weave into the body of the letter, and (2) the realities Jude prays for are gospel realities.
The gospel realities of “mercy, peace, and love” already exist among Jude’s readers, which is why he uses the word “multiply.” He hopes God will increase the impact and benefits of the gospel among the church(es) he’s writing to.
What do Jude’s readers need in order to confront the challenge the intruders pose? Not less of the gospel but more of it, more of its power and fruit. They have received mercy, so they should be ready to show mercy. They have peace with God through Christ, so they should maintain peace as the cords of fellowship are strained by wicked men. They are loved by God, and that reality should cause love to multiply in their midst.
Stating the obvious once more, Jude is praying for God to do this work. Only God can give them what they need, and what they need is the transforming realities of the gospel to expand and abound. The gospel is for unbelievers who need to be saved, and the gospel is for Christians who are saved.