It isn't a failure of Protestantism but that of Roman Catholicism that presumes there is anything within the believer - of himself - to merit or appropriate sanctification as well as justification. We were washed, sanctified and justified in the name of the Lord Jesus Christ and in the Spirit of our God. (I Cor. 6:11) We have been sanctified through the offering of the body of Jesus Christ once for all (Heb. 10:10). To assert we must suffer after death for "temporal" penalties due for our sins remaining on our souls is to negate the whole purpose of the cross. We are washed, we are sanctified, we are justified because of Christ and it is our faith in Him through which God GIFTS to us eternal life.
If Purgatory was a doctrine taught by Jesus or the Apostles - something necessary for us to know - it would have been clearly presented in God's word. It is not just our legalistic justification that we rejoice in - though that IS a major issue - but a complete imputation of Christ's righteousness for us - that everything we do we do for Him, for HIS glory, and not our own. No man may be able to boast in His presence, it is all because of grace.
The Catholic Church does not teach that we merit our sanctification; it is a pure grace. To bring up this charge is unworthy of honest discourse.
We were washed, sanctified and justified in the name of the Lord Jesus Christ and in the Spirit of our God.
If we are sanctified then we are made actually holy, not just imputed with holiness as a legalistic fiction. Are all those Protestants who have faith truly holy, i.e. reflecting the love of God and free from all attachments to sin and selfishness? If not, then "may the one who began a good work in you continue to complete it until the day of Christ Jesus."
No man may be able to boast in His presence, it is all because of grace.
Catholics also believe that it all because of grace. So where would anyone be able to boast?