John Chrysostom

"But we are bound to give thanks alway to God for you, brethren beloved of the Lord, for that God chose you from the beginning unto salvation, in sanctification of the Spirit and belief of the truth."

How unto salvation? By sanctifying you through the Spirit. For these are the things that are the efficient causes of our salvation. It is nowhere of works, nowhere of righteous deeds, but through belief of the truth. Here again, "in" is used for "through." "And through sanctification of the Spirit," he says.