If this was on-the-job training, I concluded, then the job must really be sweet

[Vladv1]

"We continued to play college fraternity parties, but soon moved up to concerts at these same universities. We were booked at a Connecticut college to open for the fast-rising Elton John and his band, and it was unforgettable. Guitarist Davey Johnstone, bassist Dee Murray, drummer Nigel Olsson, and Elton were at the top of their form and amazed everyone with their great harmonies, wonderful feel, and brilliant songs. If this was on-the-job training, I concluded, then the job must really be sweet".
"Rainbow In The Dark", Ronnie James Dio.
Could you explain the bolded sentence as applied to the context of the concert?

 

[Skrej]

Do you know what on-the-job training is?

If so, then the meaning is straightforward. "Sweet" is slang expressing satisfaction or approval, similar to 'awesome'.

 

[Vladv1]

Do you know what on-the-job training is?

If so, then the meaning is straightforward. "Sweet" is slang expressing satisfaction or approval, similar to 'awesome'.

Yes, I know. But how does it connect to the concert here?

 

[SoothingDave]

Going to the concert was part of his "training" for the "job."

 

[PeterCW]

Going to the concert was part of his "training" for the "job."

He was playing at the concert rather than "going to" it.

Playing support spots like this is an important way of gaining experience and getting your name in front of the public.