When we hear the phrase “purified conscience” our Western reflex is to think of sin, or guilt. Sin, if we have a Judeo-Christian background, or just guilt if our reference is more generically secular. Religious or not, our experience is that something bad gets “on” the conscience, and must be removed.
Not so, here. That which is being removed is “dead works” — those formerly positive sacrificial obligations of the Law, which have now been rendered superfluous by Jesus’ sacrificial blood.
So the conscience, here, is not a ledger that registers bad marks which must be removed, but is a table of positive obligations which must be…removed.