But how is such sanctifying done? Answer, “The Son receives dominion, by which He wins us, through His birth, death, resurrection, and so on. In a similar way, the Holy Spirit causes our sanctification by the following: the communion of saints or the Christian Church, the forgiveness of sins, the resurrection of the body, and the life everlasting. That means He leads us first into His holy congregation and places us in the bosom of the Church. Through the Church He preaches to us and brings us to Christ.”
Neither you nor I could ever know anything about Christ, or believe on Him, and have Him for our Lord, unless it were offered to us and granted to our hearts by the Holy Spirit through the preaching of the Gospel.
In the Word He has the Holy Spirit bring this treasure home and make it our own. Therefore, sanctifying is just bringing us to Christ so we receive this good, which we could not get ourselves.
(quotations from Lutheran Book of Concord, McCain).