Are there any sins that are unforgivable?

I’m discussing JWs because you are discussing JWs.

My comment was a response to yours (which was about JWs). And my point (about JWs) is that if they believe that God changes his mind, they that casts doubt on their entire belief system since the bible says God does not change his mind.

6 “I the Lord do not change. So you, the descendants of Jacob, are not destroyed. 7 Ever since the time of your ancestors you have turned away from my decrees and have not kept them. Return to me, and I will return to you,” says the Lord Almighty.

“But you ask, ‘How are we to return?’

8 “Will a mere mortal rob God? Yet you rob me.

“But you ask, ‘How are we robbing you?’

“In tithes and offerings. 9 You are under a curse—your whole nation—because you are robbing me. 10 Bring the whole tithe into the storehouse, that there may be food in my house. Test me in this,” says the Lord Almighty, “and see if I will not throw open the floodgates of heaven and pour out so much blessing that there will not be room enough to store it. 11 I will prevent pests from devouring your crops, and the vines in your fields will not drop their fruit before it is ripe,” says the Lord Almighty. 12 “Then all the nations will call you blessed, for yours will be a delightful land,” says the Lord Almighty.

Numbers 23:19 God is not human, that he should lie, not a human being, that he should change his mind. Does he speak and then not act? Does he promise and not fulfill?

13 When tempted, no one should say, “God is tempting me.” For God cannot be tempted by evil, nor does he tempt anyone; 14 but each person is tempted when they are dragged away by their own evil desire and enticed. 15 Then, after desire has conceived, it gives birth to sin; and sin, when it is full-grown, gives birth to death. 16 Don’t be deceived, my dear brothers and sisters. 17 Every good and perfect gift is from above, coming down from the Father of the heavenly lights, who does not change like shifting shadows. 18 He chose to give us birth through the word of truth, that we might be a kind of firstfruits of all he created.

You define it; it’s your belief. I’m just repeating what Christians say.