Thank you for the question.
I wouldn't rely on this text as a proof text for Purgatory but rather to show God expects us to be accountable through and through.
For Purgatory, in a better sense, look to 1 Peter 3:18-20 and 1 Corinthians 3:15.
In the former, Jesus preaches to spirits in a state not fit for Heaven, but not damnable. They are awaiting the fullness of redemption. There has to be the possibility of a third state besides Heaven and Hell for that to be true. In the latter verse from Corinthians, Paul talks about being saved but only as through fire. All our works are tested and what we cling to that is not of God must be burned away; we suffer loss, but are saved, for the cleansing refines us like Gold.
You can also point to Revelation 21:27, where it is pointed out that nothing unclean enters Heaven; we believe that God not only justifies us but that He completely sanctifies us before He brings us into His Abode. He doesn't bring in snow covered dung heaps like some legal farce, as Luther would suggest. His Word is effectual, and He effects our sanctification completely, and Heaven is the finality of that transformation that God carries out.
- Ask your Protestant friend if he thinks we are going to take all our garbage into Heaven?
- Then ask him if he knows anyone that achieved perfection before death?
- So is God going to leave us half-baked or will He finish the job?
That is what they must ponder.
- Purgatory is not a second chance
- it is not some scam for the Catholic Church to extract money for indulgences, though some have believed that and practiced that, to their own peril.
It is the completion of God's Work in those he is [justifying/sanctifying] through His grace.
- we can get to the work of cooperating with God for our sanctification now, or
- we can draw the process out more — through our passage into his Heavenly Kingdom
but either way, He does not abandon His children who he has called home.
Purgatory is some of the best news we have, for we know God will not let us stay like this forever.