Be all the world to somebody
Definition 1 of 1
Pro Tip 1/3Emotional Intensity
Suggests deep emotional connection, not just general importance. 
After the rescue, the firefighter was all the world to the family.
Pro Tip 2/3Hyperbolic Expression
It's often used to exaggerate feelings metaphorically, not to be taken literally. 
To the smitten poet, his muse was all the world to him.
Pro Tip 3/3Personal Importance
Shows unique personal value, rather than public or financial value. 
For the lonely sailor, his ship was all the world to him.