Is it not dangerous to know for sure that your sins are forgiven? Is it not better to keep doubting that, so that you remain humble?

Luther:

No, because that is unbelief and that can never be good. You have to rid yourselves of theologians who teach that it is good to be uncertain if we have received God’s grace and if He is our God and if we are His people.

If every Christian should be full of pious doubt, then there remains nothing of faith in the holy church and the communion of saints. Because I may not assure myself that I am a saint and you also cannot assure yourself and noone can himself – than we are all uncertain.