God chose what is low and despised in the world, even things that are not, to bring to nothing things that are, so that no human being might boast in the presence of God. He is the source of your life in Christ Jesus, whom God made our wisdom and our righteousness and sanctification and redemption. Therefore, as it is written, "Let the one who boasts, boast in the Lord." (1 cor 1:28-31)
I often think that our sanctification is very much like our original conversion experience. The more we grow in grace, the more we lose all confidence in ourselves. It seems, somewhat ironically, that as Christ works sanctification in us, the greater is our recognition of our own sinfulness. And it seems this is done for a purpose, for as we come face to face with our own corruption, we are driven to Christ as our righteousness, holiness and redemption, our all in all...our only hope before God. So sanctification is not so much about our own spirituality as it is about Christ and Him becoming greater. Christ commanded us to partake of Communion "till He come" and perhaps the reason for this is to continually focus our eyes less on what we do for Him, and more on what He has done for us and relish it. What we do in response to Him is only penultimate or secondary. The most critical error we make as believers is to look in ourselves for something that can only be found in Christ.