"The blasphemy of the Spirit": The sin here spoken of is that blasphemy, by which the Pharisees attributed the miracles of Christ, wrought by the Spirit of God, to Beelzebub the prince of devils. Now this kind of sin is usually accompanied with so much obstinacy, and such wilful opposing the Spirit of God, and the known truth, that men who are guilty of it, are seldom or never converted: and therefore are never forgiven, because they will not repent. Otherwise there is no sin, which God cannot or will not forgive to such as sincerely repent, and have recourse to the keys of the church.
 "Nor in the world to come": From these words St. Augustine (De Civ. Dei, lib. 21, c. 13) and St. Gregory (Dialog., 4, c. 39) gather, that some sins may be remitted in the world to come; and, consequently, that there is a purgatory or a middle place.
Thank you for providing this quote from St. Matthew 12. Reading this chapter in context, we can clearly see that Christ condemns these Pharisees who are committing the sin of blasphemy against the Holy Spirit.
But if I by the Spirit of God
cast out devils, then is the kingdom of God come upon you.
The Spirit of God is the Holy Spirit, thus the Pharisees are sinning against the Holy Spirit because it is through the Holy Spirit that Christ is casting out demons.http://www.drbo.org/x/d?b=drb&bk=47&ch=12&l=32-32&q=1#x
Then was offered to him one possessed with a devil, blind and dumb: and he healed him, so that he spoke and saw. 
And all the multitudes were amazed, and said: Is not this the son of David? 
But the Pharisees hearing it, said: This man casteth not out the devils but by Beelzebub the prince of the devils. 
And Jesus knowing their thoughts, said to them: Every kingdom divided against itself shall be made desolate: and every city or house divided against itself shall not stand. 
And if Satan cast out Satan, he is divided against himself: how then shall his kingdom stand? 
And if I by Beelzebub cast out devils, by whom do your children cast them out? Therefore they shall be your judges. 
But if I by the Spirit of God cast out devils, then is the kingdom of God come upon you. 
Or how can any one enter into the house of the strong, and rifle his goods, unless he first bind the strong? and then he will rifle his house. 
He that is not with me, is against me: and he that gathereth not with me, scattereth. 
Therefore I say to you: Every sin and blasphemy shall be forgiven men, but the blasphemy of the Spirit
shall not be forgiven.