Faith is never a work, if we are talking about the faith in Christ mentioned in the Scriptures.
Those who say or claim it is, are doing a number on you.
This is a straw man fallacy.
In Romans 4:16, it says "Therefore it is of faith that it might be according to grace..."
The Bible does not say nor imply at any time that your faith in Christ is something you have generated out of your shear self.
If you are saved through faith, says St Paul in Romans 4, then you are saved by grace. Faith in Christ is always according to grace.
If your saved by your faith then so say the straw man accusers - then you can have faith in your faith. Faith in Christ cannot be faith in something else, by the definition of Scripture. Stick to that definition, the accuser is doing a fallacy he himself does not recognize he is making.
If you say I have decided to believe in Jesus, then you are just fooling yourself, your faith is not a decision you cannot decide about Jesus dying for you. You can deny it and so claim that God is a liar but when you are convinced by it, the HS produced it on you.