The meaning of Vividarium et Intervigilium et Viator is In the Garden Sleeps a Messenger.
Ultimecia is the one who make that painting.Ultimecia painted a Man sleeps in the garden.And this man is a messenger.
Garden represents Viator’s life in the perspective of Ultimecia.
If you look at the face of that Man you will actually see Squall’s face.
YES The Man in that painting IS Squall in the eyes of Ultimecia.That Man represents Squall.
Viator IS Squall Leonhart.
Viator sleeps and he will wake up someday to deliver message.
Squall Leonhart ; Sleeping Lionheart.
This Lion/Squall will wake up someday.
It’s a bad situation if you know the Lion is awake. This Lion/Squall will KILL You/Ultimecia if He/Squall wakes up.
Remember Odin said “The Heaven hath decreed Thy Fate PERISH BY MY SWORD!”(btw this is not the case I just take the example)
if you fail to fight Odin after time is over.
It’s the same thing,"Squall will decree Ultimecia’s Fate PERISH BY HIS SWORD!"
So Squall is Messenger of Fate for Ultimecia.
That Message/Secret is Ultimecia’s Fate.