I have gone through your question. Its common question asked by Git beginners.
Let me explain you why the Git is asking for the commit message to you now: I can think about 3 possible reasons behind it:
You must have updated your git client recently.
Or you might never had the local branch which was ahead of a remote before.
Or you must have changed the git config very recently.
As your local repository is ahead by one commit now the git tries to merge the remote to the local repo. This procedure can be done with the help of merge but particularly in your case, I guess you are looking for the rebase means you want to add your commit to the top. This can be achieved with below command:
git rebase or git pull –rebase
Hope it fixes your issue.