according to the foreknowledge of God the Father, in sanctification of the Spirit, that you may obey Jesus Christ and be sprinkled in his blood: Grace to you and peace be multiplied.
This is probably an allusion to covenant ratification (cf. Exodus 24:5-8). Jesus’ blood was the ratification of the New Covenant (cf. Matthew 26:27-28; Mark 14:23-24; Luke 22:20) since it was the basis for the forgiveness of sins (as promised in Jeremiah 31:31-34). [Note: Buist M. Fanning, "A Theology of Peter and Jude," in A Biblical Theology of the New Testament, pp. 441-42.] 