Here is the transformation: in selecting Starmer, Labour in all its divisions shows it has at last emerged as a serious party determined on seeking power.
The article concludes with a reprisal of the decisive tone it began with. ‘At last’ as a preposition suggests that change has long been needed: Starmer’s leadership has rectified the Labour Party to a ‘serious party determined on seeking power.’ Seriousness and determination (the former used as a pre-modifying adjective, the latter as a stative verb)= qualities the reader finishes the article admiring.