But we are bound to always give thanks to God for you, brothers loved by the Lord, because God chose you from the beginning for salvation through sanctification of the Spirit and belief in the truth;
Through sanctification of the Spirit - Being made holy by the Divine Spirit. It is not without respect to character, but it is a choice to holiness and then to salvation. No one can have evidence that he is chosen to salvation except as he has evidence that he is sanctified by the Spirit; see the notes on Ephesians 1:4.