The answer is: a proverb which was excerpted from Rob Goldston and it represents a short phrase aimed to understand relationships.
The other options do not apply because of the following reasons:
This is not a love note because it implies a relation with any person (not with the one you love).
This is not an invitation because it doesn't have any verb inviting someone.
It is not an apointment reminder because it doesn't say anything related with a date.