It always comes back to baptism. Every time we baptize, the following words (or something like them) are said:
In baptism God claims us, and puts a sign on us to show that we belong to God. God frees us from sin and death, uniting us with Jesus Christ in his death and resurrection. By water and the Holy Spirit, we are made members of the church, the body of Christ, and joined to Christ’s ministry of love, peace and justice.
Sanctification is the process of growing into all these hopes and promises.