Matthew 12:31-35

Mat 12:31 (KJB)
Wherefore I say unto you, All manner of sin and blasphemy shall be forgiven unto men: but the blasphemy against the Holy Ghost shall not be forgiven unto men.

Jesus now refers back to what was previously spoken by means of “Wherefore.” He is stating that all kinds of blasphemy and sin are forgivable sins and those who are the Elect of God will have those sins forgiven because in all of our lives, we have committed heinous sins of blasphemy. Then Jesus states in no uncertain terms that blasphemy against the Holy Ghost will never be forgiven. What the Pharisees had just done was to proclaim that the miracles that Jesus did such as delivering a man from the power of Satan was done by the power of Satan. The miracles of Jesus were done under the power of the Holy Spirit and the Holy Spirit is the third person of the Godhead, fully God. What they were saying was that the miracles Jesus did was under the power of Satan, thus stating that the Holy Spirit was an unclean Spirit akin to Satan himself. This would mean that they were also saying that if the Holy Spirit was an unclean Spirit, that would make God the Father an unclean Spirit since the Holy Spirit was eternal God Himself. This was blasphemy of the highest order and was a sin that was not forgiven.

Mat 12:32 (KJB)
And whosoever speaketh a word against the Son of man, it shall be forgiven him: but whosoever speaketh against the Holy Ghost, it shall not be forgiven him, neither in this world, neither in the world to come.

Here Jesus includes Himself that those who speak against Him will be forgiven. The Apostle Paul is a great picture of this forgiveness. To not understand that Jesus was divinity in human flesh is understandable. Then Jesus re-emphasizes that fact that those who equate the Holy Spirit with being an unclean spirit, will never have forgiveness here or in eternity. This shows that the depth of human sinning can cross a barrier from which there is no forgiveness.

Mat 12:33 (KJB)
Either make the tree good, and his fruit good; or else make the tree corrupt, and his fruit corrupt: for the tree is known by his fruit.

There is no middle ground when it comes to sin. Either the person is saved and you know that by the good fruit they exude or the person is unsaved and that is known by the bad fruits they exude. Jesus specifically targeted the Pharisees since their fruits were corrupt because of the way they had rejected Him and believed that He was under the power of Satan. (James 3:12 KJV) Can the fig tree, my brethren, bear olive berries? either a vine, figs? so can no fountain both yield salt water and fresh. The reality is that either you are saved yielding fresh water or you are not, yielding salt water. One can tell this kind of person because they are seen in church on Sunday and the bars on Saturday night. On Sunday morning he plays Christian but the real him is on Saturday night.

Mat 12:34 (KJB)
O generation of vipers, how can ye, being evil, speak good things? for out of the abundance of the heart the mouth speaketh.

John the Baptist also called the Pharisees a generation of vipers. This would place the Pharisees in the camp of Satan since Satan is referred to as a serpent. (Rev 20:2 KJV) And he laid hold on the dragon, that old serpent, which is the Devil, and Satan, and bound him a thousand years, Jesus then directly tells them that they are evil because they thought their righteousness was irreproachable. It would be impossible for them to speak of the things of God such as salvation and the Lord Jesus Christ in a proper biblical manner because they were unsaved and were hostile to the Gospel. Their hearts were darkened with the blackness of sin and as a result, their evil heart was manifested publicly by the words they spoke and the actions they took against Jesus and the truth. If the heart is darkened by sin, then the words which are spoken will be darkened by sin.

Mat 12:35 (KJB)
A good man out of the good treasure of the heart bringeth forth good things: and an evil man out of the evil treasure bringeth forth evil things.

Then Jesus makes the comparison that those who are saved and have a heart which is filled with light will bring forth the good things such as salvation, eternal life in Christ, the indwelling of the Holy Spirit. Those who have an evil heart will be deprived of knowing the truth and this will result in blasphemous teachings, lies, hatred, and false accusations.