There is no Scriptural basis for purgatory. Jesus never taught of such a place, and neither did the disciples or Paul. Purgatory is a teaching and doctrine of the Catholic Church.
So who is it that actually forgives sin? Where does the forgiveness for sin truly come from? From man, or from God?
How can we possibly "make up for our sins"? This sounds like the Old Testament law and sacrificial system to me. As people saved by Christ, we are no longer under the Law, and it is Christ who saves us, not our own efforts.
Yes, we acknowledge and take responsibility for our sins, and we do this when we repent and seek forgiveness from the only One Who can save us, Jesus Christ. We are lost in our sins without Him, no matter what we do, and nothing we can do adds to His work on the cross for our salvation.
And yes, sometimes we will face dire consequences here in this life for our sins, but that is not the same as Church imposed teaching and instruction that we must do something to make ourselves right with God. The only thing we can do is accept by faith His forgiveness and salvation, turning from our sins and repenting. No additional works will purify us or save us, believing such things is to put us back under the Law.
Again, the natural consequences that we must at times face in this life as a result of sin, are indeed often God's discipline of us. Penance is entirely different however, as penance is done to atone for our sins. This is completely unnecessary and pointless, because Christ has already atoned for all of us, once for all time, and His sacrifice and atonement are absolutely sufficient for us. We have been made right with God through Jesus Christ, not by anything we have done or will do.
Please provide Scripture that clearly supports these claims. Where in Scripture does it say that our souls must go to a place where they will be purified? Or that even after calling upon the name of Jesus to be saved, trusting in His forgiveness, we will still die with "sins on our soul" and that we need to go to purgatory to "have them cleaned"?
Is Christ's work on the cross, His death and resurrection sufficient or isn't it? Where in Scripture is it taught that more must be done to purify our souls? Where is this doctrine of purgatory found in the Bible?
The process of purgation is spelled out in 1 Cor. 3:11-15. The verses speak of God's judgement
after death.
Clearly forgiveness of sins only comes from God, yet just as clearly, Jesus gave this gift to His apostles: John 20:21-23. This did not die with the physical death of the apostles, as shown in Acts 1, where the office that Judas held was refilled. No sins are forgiven without Christ.
Atonement for our sins, known as penance, is also taught in the New Testament in multiple places. You correctly state that Christ has paid the penalty, and our sins have been atoned for and it is not our personal atonement that 'makes up for' our sins, but it is the uniting of our shortcomings (sins) with Christ that allows for our sins to be paid for as it were by Christ. This can be seen in Hebrews 12:5-13. Our personal penance accomplishes exactly this unity with Christ. You yourself recognize this when you state above that we must repent and seek forgiveness from God, and when you further state that God sometimes presents us with dire circumstances as a means of discipline. Since Christ founded the Church, and Christ gave His voice to the Church, (whomever hears you, hears me) it is perfectly reasonable to conclude that, as you put it, the Church imposes teaching and instruction as a means to 'get right' with God. You are partially correct when you say that the only thing we can do is repent and seek forgiveness...but, as the passage in Hebrews tells us, we can, and should also submit to His discipline.
Penance is much like a parent grounding a child for misbehavior: the sin of misbehaving is forgiven, yet the child, in order to better understand that there are consequences for the sin, must undergo punishment and ultimately, must see and turn from (repent) the error. In the New Testament, one example of penance (offered by Jesus, the apostles and St. Paul) is fasting. Fasting is a means of humbling (humiliating) ourselves before The Lord. And this is the heart of what penance is: a humbling of ourselves before God; acknowledging that we are incapable of saving ourselves. We fall at His feet and beg forgiveness. (See Mark 2:18-20; Acts 13:2-3; Acts 14:23; James 4:8-10)
We are also called by St. Paul to view our sufferings as penance, and as a means to unite our personal suffering to Christ: we see this in 2 Cor. 1: our sufferings are our penance, and this is exactly what even allows us to see the great comfort that God provides. Phillipians 3:10 and 4:12 show us the our sufferings draw us closer to Christ. Penance, in Catholic teaching, is voluntary suffering, an act of our free will that is part of our repentance and turning from our sins and towards Christ. It is, as you say above, our accepting of what He has done for us, not an effort to make ourselves justified, but rather our admittance that we can accomplish nothing for salvation unto ourselves and that we are fully willing to submit to His will.
As to your question about Christ's cross, death and Resurrection being sufficient: St. Paul mentions this with both a 'Yes', and a 'Not quite' answer: His suffering, death and Resurrection are easily more than enough on their own. (Multiple entries throughout his writings). But he also says that Christ desires us to unite our own personal sufferings with His through the Church, going so far to say that Christ sufferings were 'lacking'(!) in Col. 1:24. This fits seamlessly with the Churches teachings that penance, as a means of humbly presenting ourselves before God, is a very real way for us to grow in our personal relationship with Christ. St. Paul even tells us to accept this joyfully (as he himself did) in order to 'know' that we are truly submitting to His will.
Penance only = punishment if we fail to view God's discipline as a gift and a means to grow IN Him
Hope that helps
Peace in Christ
Hawkiz