First John 1:7 says that the blood of Christ frees us from all our sins. Why then is there a need for Purgatory, if it is, as you say, "a place of purging, of purifying oneself of our sins." Isn't the good news of the Gospel that we have been purified already when Christ is accepted as our savior?
Yes, receiving our Lord Jesus Christ in Holy Communion, does free us from our venial sins. However, even before we receive our Lord, our venial sins are forgiven in the penitential rite at the very beginning of the Mass. On we can't forget that anyone in the state of Mortal sin is prohibited from receiving Communion until such time as they can confess their sins and be forgiven in the sacrament of Reconciliation.
This being said, anyone in the state of Mortal sin when they die is in need of purgatory. Even those not in the state of Mortal sin, may still be in the need of purgatory, because most of us commit venial sins are a fairly regular basis.... Scripture tells us that even a good man will sin on average of seven times a day, just think how much more for the not so good man, or even the bad man.