The happier version of Jon Snow
Why is it definite and not indefinite?
Mai rapizi, vă rog!
Anybody know why subject and verb are inverted here?
Can't it mean "he/she/it comes in Spring"
For the same reason you wrote "in" Spring. It would need a preposition in order to imply that an unwritten subject is coming "in" Spring rather than Spring itself coming.
Spring requires a preposition because it's a noun. The adverb primăvara doesn't need one.
To GlennEvani re "Joy to the world, the Lord is come!" Yep. Written by Isaac Watts in 1719, when it was still the norm to say "is come" instead of "has come".