Secure booting Error
Cause : boot certification verify
The phone is rooted LS970
What am I missing
You can't boot straight to recovery? What do you mean when a rom is installed it gives you that error? If I remember right that is because the bootloader is still locked. Have you tried the hard recovery boot combo? I think it is power and volume up, then you should see bootloader, volume up and down change the options, when it says recovery press the power button.
Check this thread for brick repair,
It will help you get into recovery and have a rom installed.
If you are looking for stock I suggest this thread for the rom once you can get into recovery.