How do you know your prayers will condemn you?

Psalm 109:7 says may his prayers condemn him. What does this verse mean? and did the satan have salvation too but he chose to walk away from it? because it doesn't say we can lose ours. I thinking maybe it was different for him than it is for us. Anyone know for sure? I'm afaraiad to lose mine, but I don't think you can cause it is a promise from God that you will be forever sealed with the Holy Spirit. Ephesians 1:13, just curious