Read the dictionary definition of surely. All definitions for this word.
1. definitely or positively (`sure' is sometimes used informally for `surely')
1. the results are surely encouraging
2. she certainly is a hard worker
3. it's going to be a good day for sure
4. they are coming, for certain
5. they thought he had been killed sure enough
6. he'll win sure as shooting
7. they sure smell good
8. sure he'll come