Gmail Notification stopped working on Nexus 4 I have to press the refresh option in Gmail just to get new messages.

I have checked the application and the notification setting is on. I stopped it and then again started it but still it is not working. Is anyone else facing such issue? Android version is 4.2.1

In my accounts it is showing that "Sync is OFF". Has this something to do with this? I always see this option like this and have to go inside it to change Gmail, Currents, Photos, etc. to sync.
On stock Android 4.2.2 on my Galaxy Nexus I had the same problem of gmail notifications not working. I checked that in Settings>Data Usage "Auto Sync" was turned on. 

Then I went to Settings>Accounts>Google, hit the email address and you see everything that is being synced or not. 

Weirdly for me it Gmail sync was inactive after I had recently updated my rom. 

This should take care of this problem.