Most Catholics are familiar with the term mortal sin. Mortal sins deprive the soul of grace. They are serious transgressions of God's law, done freely and deliberately with a clear understanding of what they are. Their result is to deny a soul entrance to heaven.
There are particular mortal sins that are so evil that they are said to be sins that cry to heaven for vengeance: murder (Gn 4:10), sodomy (Gn 17:20-21), oppression of the poor (Ex 2:23), and defrauding workers of their just wages (Jas 5:4).
Sins against the Holy Spirit are mortal sins that harden a soul by its rejection of the Holy Spirit. Six sins are in this category. They are despair, presumption, envy, obstinacy in sin, final impenitence, and deliberate resistance to the known truth.