Terrible intrusive thoughts and blasphemous thoughts I do not want

Unwanted, intrusive thoughts - including shocking or blasphemous ones that horrify you - are not the same thing as sin you have chosen, and the horror you feel at them is actually evidence they are against your will, not from it. Temptation itself is not sin: Jesus 'was in all points tempted like as we are, yet without sin' (Hebrews 4:15), and thoughts fired at the mind are described in Scripture as 'fiery darts of the wicked' to be blocked with the shield of faith (Ephesians 6:16) - darts imply an attacker, not a traitor. Sin is what we welcome, feed, and act on (James 1:14-15), not what ambushes us and is refused.

Fighting intrusive thoughts by arguing with each one usually strengthens them; Scripture's pattern is redirection - 'whatsoever things are true... think on these things' (Philippians 4:8) - and casting the anxiety itself on God (1 Peter 5:7). One more important word: when intrusive thoughts become relentless, ritualistic, or center on the fear of having sinned unforgivably, that pattern is well known and very treatable (it is often scrupulosity, a form of OCD) - a counselor who understands it can bring enormous relief, and seeking that help honors God.

You are not a monster. You are under fire, and God is your shield (Psalm 3:3).