Luke 23:43 KJV And Jesus said unto him, Verily I say unto thee, Today shalt thou be with me in paradise.Unless Jesus was lying to the thief, then this notion of purgatory seems problematic.
...And because this was a matter of great importance, and an instance of amazing grace, that so vile a sinner, one of the chief of sinners, should immediately enter into the kingdom of God, and enjoy uninterrupted, and everlasting communion with him and that it might not be a matter of doubt with him, or others, Christ, who is the "Amen", the faithful witness, and truth itself, prefaces it after this manner: "verily I say unto thee"; it is truth, it may be depended on. This instance of grace stands on record, not to cherish sloth, indolence, security and presumption, but to encourage faith and hope in sensible sinners, in their last moments, and prevent despair. The Papists pretend to know this man's name; they say his name was Disma; and reckon him as a martyr, and have put him in the catalogue of saints, and fixed him on the "twenty fifth" of March.Given that these were among the last words Jesus spoke in His ministry and this thief was the last sinner He evangelized, I trust we can take Him at His word. That so much of the doctrines of grace are confirmed from this single statement by our Savior is a blessed teaching to us and an assurance of our security in Christ. Our Savior will save us as scipture promises and He has paid our full ransom in His own blood, once and for all.
(The story of the penitent thief has sometimes been considered the most surprising, the most suggestive, the most instructive incident in all the Gospel narrative. ... In the salvation of one of the thieves, vital theology finds one of its finest demonstrations.
Sacrementalism was refuted, for the thief was saved without recourse to baptism, the Lord's Supper, church, ceremony, or good works.
The dogma of purgatory was refuted, for this vile sinner was instantly transformed into a saint and made fit for paradise apart from his personal expiation of a single sin.
The teaching of universalism was refuted, for only one was saved of all who might have been saved. Jesus did not say, "Today shall ye be with me in paradise", but "Today shalt thou be with me in paradise."
The notion of soul-sleep was refuted, for the clear implication of the entire incident is that the redeemed thief would be in conscious fellowship with his Saviour in paradise even while his body disintegrated in some grave.
Too, it is doubtful whether any other gospel incident presents the plan of salvation more clearly or simply.--Dr. Charles R. Erdman)
The poster, himslef a Calvinist like you, asked not to engage in theological debate. However, what you posted regarding the Good Thief is inaccurate.
First, because Christ told one man that his stay in Purgatgory will be either less than a day long, or nonexistent, does not mean that everyone else's stay in Purgatory will be less than a day long, or nonexistent.
Second, the Good Thief did satisfy the necessary requirement to enter heaven: he repented of his sin, he was baptised by blood through his painful death, he did a good deed of defending an innocent, and he died with his gaze fixed on Christ Himself, thus in sacramental communion with Him. The aftereffect of his sin (of theft, we presume) was purified by his suffering on earth, thus no purgatorial sufferign was necessary in his case.
Lastly, the Church and ordinary sacramental life available through it has not been established yet; that happened at the Pentacost.
Most likely your dad is right now enjoying the splendor of being in the presence of God and smiling that you had it right all along.