No the concept of Purgatory is not "extra Biblical".
One passage that I think is important to the discussion is Hebrews 12:3-14. This is the RSV translation. Shortened a bit for brevity but you can easily read the entire passage if you wish. Note that different translations will vary with language – “discipline, punishment, chastisement”. All mean the same thing.
7 It is for discipline that you have to endure. God is treating you as sons; for what son is there whom his father does not discipline? 8 If you are left without discipline, in which all have participated, then you are illegitimate children and not sons. 9 Besides this, we have had earthly fathers to discipline us and we respected them. Shall we not much more be subject to the Father of spirits and live? 10 For they disciplined us for a short time at their pleasure, but he disciplines us for our good, that we may share his holiness. 11 For the moment all discipline seems painful rather than pleasant; later it yields the peaceful fruit of righteousness to those who have been trained by it….. 14 Strive for peace with all men, and for the holiness without which no one will see the Lord.
You may ask, what does this have to do with Purgatory when it is most certainly talking about the Lord’s discipline in our life right now? I think it’s important to the discussion because it negates the idea promoted by some that once we accept Christ’s “finished” work on the cross there is no longer any punishment or discipline due to us related to our sin. This is not true. Christ’s sacrifice on the cross removes the
eternal consequence of sin – eternal separation from God. It does not negate discipline or punishment related to our sins in the temporal sense. And this passage shows us some important things. God disciplines us for our own good and this is necessary so that we may share his holiness, and we should strive for this holiness for without it we will not see the Lord.
The question then becomes whether or not we all achieve this holiness in this lifetime. I often turn to this evangelical site when I want a perspective different than the Catholic one. And it says this:
In the final analysis, there is nothing in Scripture that teaches that believers will become perfect in this life. Entire sanctification will take place when we reach heaven, but not until. The expectation is that believers on earth will continue to sin and need to be cleansed (1 John 1:9). It is realistic to expect that Christians will not live in conscious sinful rebellion against God, but sin is too pervasive to ever escape its contaminations in this life.
What is entire sanctification? Is it possible to be entirely sanctified in this life? Is the doctrine of entire sanctification biblical?
www.gotquestions.org
This Christian author indicates that our sanctification will be completed when we reach heaven. As a Catholic I would simply disagree with him, it is completed on our way there – Purgatory.
Then we get to 1 Corinthians 3:11-1515
11 For no other foundation can any one lay than that which is laid, which is Jesus Christ. 12 Now if any one builds on the foundation with gold, silver, precious stones, wood, hay, straw— 13 each man’s work will become manifest; for the Day will disclose it, because it will be revealed with fire, and the fire will test what sort of work each one has done. 14 If the work which any man has built on the foundation survives, he will receive a reward. 15 If any man’s work is burned up, he will suffer loss, though he himself will be saved, but only as through fire.
The ”Day” when our works our revealed and tested is clearly our judgment day.
There are those (including some in this thread) who want to insist this is about our works alone being consumed in the fire and has nothing to do with the person. But verse 15 pretty clearly states that “If any man’s work is burned up, he will suffer loss,
though he himself will be saved, but only as through fire”. Clearly we are not a mere “observer” in this purification by fire but our person is the object of it.
I know you asked for brevity for topics like this can’t be handled with a random Scripture or two tossed out. It’s a concept, and Purgatory is indeed a quite Biblical concept. But to summarize in brief
1) God punishes/disciplines/chastises us according to the sin in our lives for the purpose of bringing us to share in his holiness (Hebrews 12:10)
2) This process is not pleasant and can be painful (Hebrews 12:11)
3) We are to strive for this holiness and will not see God until we attain it (Hebrews 12:14)
4) There is nothing in Scripture that indicates this state of entire sanctification or holiness will be completed in this life
5) After our death we will be saved, but only as through fire as our works of stubble are purged from us. (1 Corinthians 3:15). God will complete our process of sanctification until it is thoroughly completed and all traces of sin have been purged from us.