won’t start unless it’s started by the starter?

Most cars only start with the starter, unless you have a Model T or similar. Or do you mean the key or remote start doesn't work? Battery light and security light both sound like you have a battery that has an issue. Did this happen after the body module swap or was it swapped trying to repair it?

It won’t start with the key. & this happened about a year after the bcm swap.

I just went into the store and it wouldn’t start. & the battery was loose but it isn’t anymore. Is there a procedure to unlock the security system on an 01 Chevy impala?

OK, so it was running OK and then you stopped one day and it wouldn't start again. What does it do when you turn the key? Nothing? Turns over and doesn't run or turns over and runs a couple seconds then stalls? Does the security light come on? Or flash?
The description doesn't sound like security at this point.

When I turn the key it just pops up the battery light, the security light, and oil light
on my little messages box on the dash. And it doesn’t start. It was out of nowhere honestly.

OK, the lights coming on like that would be the bulb test, from there the engine would normally start and they would go off. However, in your case the car isn't starting so nothing happens. This can be multiple things, but it isn't the security system as it would let the engine start run for about 3 seconds and then stall because it disables the fuel system.
You can start with the sections in this guide. Being it was out of nowhere I would look at the battery connections then the starter relay.
https://www.2carpros.com/articles/car-cranks-but-wont-start