First, I will give a short explanation, then I will give you some more verses to support the Church teachings, and finally explain why Jesus' death is sufficient for redemption, justification, but it's up to us to apply it for sanctification (they are complimentary, but separate things).
We’ve read that it’s God’s will that we get to heaven (see 1Thess. 4:3), but Rev. 21:27 states, "Nothing unclean shall enter heaven." This is because the only love that can be in heaven is God’s love-perfect love as this is the only love that is worthy of humanity; the love we were made for (see Gen. 2:7 man is only creature which God "breathes in His Divine Spirit-we call this inspiration- and since God is love-1Jn. 4:8-God gives us life by making us for His love-also the entire point of the Sabbath, for God to rest within us). So to fulfill God’s will for our lives and at the same time His Justice, we must be cleansed of anything (sin, imperfection) that is not perfect love. As one little speak of mud ruins a glass of water, so too, the slightest imperfection must be purged before heaven. Or as St. John of the Cross says, the slightest thing tied to a bird will keep it from flight. So our flight (heaven) is kept if we are attached to even the slightest thing. So we must be cleansed or detached in this life or the next. Mt. 12: 31-32 speaks of sins against the holy Spirit not being forgiven in this age or the next showing that some sins can be forgiven or purged in the next life. The place of purging (cleaning) and making reparation after this life is called purgatory. It prepares us to enter into God’s love!
· *2Macc. 12:44-46 (we see the practice of praying for the dead to make up for their temporal punishment-it is a Jewish practice that Catholics continue)
· *2Sam. 12:1-14 (David commits a horrible crime. God forgives him in verse 13, so "he will not die"-physically or eternally, but note he still has to make up for his adulterous act
· *1Cor. 3:15-the verse cited speaking of being cleansed by fire
· *1Pet. 3:18-20; 4:6-Jesus preached to the souls of the dead or "in prison". These dead souls in prison could not be the souls of the damned as they have eternally rejected God through their own free will, thus preaching to them would have been useless. There must be some dead souls suffering who would have listened to Jesus. These are the souls in purgatory
Isn't Jesus' death Sufficent
Yes, Jesus opened up the gates of heaven and made us right with God. This is justification (see Rom. 5:1-10). But it doesn't stop there as justice must lead to charity (love) as God is love. We now, because of Jesus' death on the cross have the possibility of heaven once again, but we "must work out our salvation with fear and trembling" (Phil. 2:12-13) because "God will repay everyone according to his works" (Rom. 2:6-8). Our applying God's grace and merit to our lives so that we will be transformed into the perfect imitation of Christ and do everything for the Lord (see 1Cor. 10:31; 11:1). In doing so we participate in our own happiness, salvation, and as St. Paul says, "build up his [Jesus'] body (Eph. 4:12) and "make up in our sufferings what is lacking on behalf of the afflictions of Christ" (Col. 1:24). This is called sanctification. Note that in this chapter, you see the answer to this seeming contradiction. The first part (Col. 1:1-23) speaks of Jesus and Him giving us reconciliation (justification). This is passive, primary, and something we receive. It is a free gift that none of us can do. Then only once we receive this gift (in Latin this is where the word "grace" comes from) can we use it, apply it to ourselves and give it to others. This is the second part of the chapter (Col. 1:24-29) and this is sanctification. In other words, God's love impels us to live and share his love with others. St. John sums this up beautifully when he says, "In this is love: not that we have loved God, but that he loved us and sent his only Son as expiation for our sins [justification]. Beloved, if God so loved us, we also must love one another. No one has ever seen God. Yet, if we love one another, God remains in us, and his love is brought to perfection in us [sanctification] (1Jn. 4:10-12). Justification must lead to sanctification because God didn't just want us to be free from sin. He wanted us to be fulfilled by being with Him, to dwell in the love that we were made for, and in doing so, be PERFECTLY HAPPY (which just being free from sin could not do for us). This is sanctification and God's will for all of us (see 1Thess. 4:3) Hope this helps. God bless.