Which are the sins that will not be forgiven in the age to come?
"Whoever speaks a word against the Son of Man will be forgiven, but whoever speaks against the Holy Spirit will not be forgiven, either in this age or in the age to come."(Matthew12:32)
From the above reference verse, it clearly distinguished the difference between sins against the Son of Man/Jesus versus the sin against the Holy Spirit.
The BIG QUESTION here is, how can you speak a word against the Holy Spirit, we all know Jesus became God-Man but the Holy Spirit did not incarnate.
Jesus addressed this to the crowd and Pharisees, saying anyone who publicly attributes the work of the Holy Spirit to the devil/satan is the "UNFORGIVABLE SIN"
As Christian we know the scriptures teaches us that our body is the temple of the Holy Spirit, and the Holy Spirit can dwell in a believer to inspire his thought,words and action.
If you are asking for Catholic perspective let me stated the reflection of St.Maximillian Kolbe about the Lourdes Apparition Mary saying "I AM" the Immaculate Conception" instead of saying I am immaculately conceived...
St.Kolbe...stated the Immaculate Conception is divine, St.Kolbe is pointing to the Holy Spirit as the Uncreated Immaculate Conception and Mary as the created Immaculate Conception (p.52 book of Fr.Gaitley 33Days to Morning Glory)
The Mystery of Truth lies in the mystical union between the Holy Spirit & Mary(as Spouse/Advocate).
What type of union is this? It is above all an interior union, a union of her essence with the "essence" of the Holy Spirit.The Holy Spirit dwells in her,lives in her. This was true from the first instant of her existence.It was always true, it will always be true.(p.53 book of Fr.Gaitley 33Days to Morning Glory)
What does St.Kolbe driving at his reflections.If Satan can possessed the body of a human submitting to his powers. Mary by Her FIAT and Total Surrender to God's WILL, enable the Holy Spirit to animates her thought, words & actions.In the words of St.Kolbe Mary is "POSSESSED/ANIMATED" completely and perfectly by the Holy Spirit.
Now from the approved Catholic Church Marian Apparition at Fatima in 1917. Sis. Lucia gave the five blasphemy against Blessed Virgin Mary.
The verse now in reference(Matthew12:32) and the words of Jesus pointing to anyone who publicly attributed the works of the Holy Spirit to the devil is the UNFORGIVABLE SIN.
The reflections of St.Kolbe on the Mystical Union of the Holy Spirit & Mary points to all approved Marian Apparitions clearly is the work of the Holy Spirit.
Please see the link below on the The Five Sins Against Our Lady:
The Five Sins Against Our Lady
"My daughter, the motive is simple: there are five ways in which people offend and blaspheme against the Immaculate Heart of Mary:
1.the blasphemies against the Immaculate Conception,
2.against her virginity,
3.against the Divine Maternity, refusing at the same time to accept her as the Mother of all mankind,
4.those who try publicly to implant in the children's hearts indifference, contempt, and even hatred against this Immaculate Mother, and
5.those who insult her directly in her sacred images.
Looking on the Five Blasphemies against Blessed Virgin Mary is a direct attack on the Holy Spirit, basing it from St. Kolbe reflections & teachings and biblically from the word OVERSHADOWED.(Luke1:35).And the Overshadowing is paralleled to the Ark of the Covenant.
Jesus affirmed this kind of direct attack when he said "Saul, Saul why are you persecuting me?"(Acts9:4)
In conclusion, Matthew 12:32 is Jesus way of protecting His Mother from all evil attacking Her Dignity and God given role as the Mother of God (Theotokos) and recently Pope Francis declared Mary as the Mother of the Church.
So those who publicly attributes the approved Marian apparitions to the devil/Satan and the five specific action directed towards blaspheming the Dignity of the Blessed Virgin Mary are the UNFORGIVABLE SIN.