It’s true the word Purgatory does not come up once in the Bible. But that’s not a reason for rejecting the idea. The word Trinity appears nowhere in the Bible but no one denies that it is taught throughout the Holy Writ. Catholics simply contend the same for the doctrine of Purgatory.
How do you explain the doctrine of Purgatory to a Christian who confronts you with it? It seems that the Protestant Christian believes that one is saved once you accept Jesus into your heart as you personal Lord and Savior (the born-again experience). This born-again experience can be explained as different processes already done in our Catholic life: How much better to accept Jesus then to take Him onto our tongues and into our very beings when swallowing the Eucharist?
Jesus’ salvific work was complete once He died on the cross. He offered Himself up as the perfect sacrifice for our sins. Jesus’ earthly work is complete, we need only ask with a perfectly repentant heart and our sins are forgiven. But what happens to our souls when we sin? Sinning ‘stains’ our soul, or it ‘muddies’ the soul, it becomes harder to see God through those stains, through the mud caused by our sins. The water in the mud is pure, but the floating dirt dims God’s rays of sunshine. Whenever you ask forgiveness with a contrite heart, you shall be forgiven, but the soul is still stained, still muddied from that sin. There is restitution to be done as we see in Luke 12:59 “…I say to you, you will not be released until you have paid the last penny”. To ‘clean’ yourself up you need to do penance (ie. Do good works for the Glory of God, read Scripture, say some prayers, etc…). These deeds are to be done only to bring you closer to God, they are not technically needed for your salvation. If you do not ‘cleans’ yourself perfectly in this life, God shall finish the job of your perfectedness by trial by fire as in 1 Cor 3:15 “But if someone’s work is burned up, that one will suffer loss (pain); the person will be saved, but only as through fire.” You need to be perfectly ‘clean’ before you can enter into the presence of God (Rev 21:27).
Most of us will never reach a level of perfect union with God in our lifetimes. How then can you ensure your salvation? You are saved! Nothing can change that short of committing a mortal sin without repenting before the end of your earthly life. Purgatory is just a way-station to clean up your stained soul before meeting the Father. There is nowhere to be read that this process is instantaneous or that it has a duration. There is no way to deny either lengths of time. Both Protestants and Catholics agree that absolute holiness is necessary to enter heaven. Disagreements arise when the question of duration comes up.
How long does this purification, or sanctification take? Some Protestants believe it is instantaneous, while Catholics believe that there is a possibility of duration involved in the sanctification process. It seems that Catholics and Protestants believe the same thing but name it differently. Because does anybody know how time works in the afterlife? How is time viewed in light of eternity? Nobody really knows, and whether it is instantaneous or not, Catholics name this process of cleansing as purgatory.