"Chosen before the foundation of the world" 🤔

Reading Ephesians 1 this morning the verse 4 says "He chose us in Christ before the foundation of the world, so that we would be holy and blameless in His sight."

There are other Bible references to being selected before the foundation of the world.

Does this mean that only certain people can ever be saved?
What about determining your own destiny?
If you are chosen, can you then sin forever and still be saved as you are predestined?

What are your thoughts on this?