"Trusting in their own works" is not much of a problem. It may be possible, but the opposite - what you do doesn't matter, all that matters is what you believe - is much worse, and clearly condemned on like, every page of the bible. So no, "I never knew you" has nothing to do with "trusting in their own works".
"Grace" is God Himself, and "faith" includes what you think and what you do. Don't bother with _sola fide,_ it's a dead end.
"Trusting in their own works" is not much of a problem. It may be possible, but the opposite - what you do doesn't matter, all that matters is what you believe - is much worse, and clearly condemned on like, every page of the bible. So no, "I never knew you" has nothing to do with "trusting in their own works".
How do you, objectively, have assurance of salvation?