“My task here as a Catholic is not to deduce the Catholic doctrine from the Scripture but rather explain the Scripture in the light of the doctrine received by the Church from the Holy Spirit directly.”
Exactly. You use scripture to prove your views, rather than letting scripture speak for itself via the Holy Spirit.
If one assumes Mary was sinless, then any verse about her can be made to mean that, and any verse saying all have sinned can be made to mean all but Mary. If you assume Purgatory, then you can force it upon scripture.
Protestants just believe that is backwards. And we cannot agree on specific arguments without first determining if Scripture is the rule, or if Catholic teaching is true because it is assumed to be true.
It is by letting the scripture speak for itself that we find out that both sinlessness and perpetual virginity of Mary make scriptural sense, and the fantasies about her being “quick to shed blood” and having given birth to God proceeding to make more little’uns like nothing happened make no scriptural sense.
Ditto for Purgatory, by the way. What do you think 1 Cor. 3:9-15 describes, AWANA class?