1. Because you are probably not now, and most likely will not be at the time of your death, perfectly free from every stain and inclination of sin. If you have even the slightest inkling to commit even the most minor sin, you have not been perfected. That perfection is required to enter heaven. Purgatory is the final fire to remove such impurities.
2. Is the prayer of the righteous man powerful or not? Does God aid those for whom we pray?
3. Hebrews is addressing the redemption of the human race, not the sanctification of each individual (this is clear from context and a plain reading). Once again you are ignoring what I have said in order to try and put purgatory in opposition to the cross. Purgation is accomplished solely through the merits of Christ’s sacrifice. This is now the third time I am stating this.