Nowhere in Matthew 12:32 does Christ make reference to “stages” in the age to come (eternal life). Essentially Christ says that if you speak against the Holy Spirit you won’t be forgiven in this lifetime or in the next lifetime. That doesn’t inherently imply that forgiveness of other kinds of sins occurs in the next lifetime. It means exactly what it says - you will not be forgiven ever for speaking against the Holy Spirit. In my opinion, there is no support in Mattew 12:32 for a concept of stages in the age to come or for Purgatory.
The author asserts that Matthew 12:32 provides evidence of Purgatory. He only cites one other New Testament verse, which I am not finished reviewing, and he doesn’t tie those two verses together. So one must assume that he intends those two verses to separately provide evidence of Purgatory.
Why didn't Jesus just say so?
You intention to read to the end of the article is good. Let me know how you do.