What is ‘modernising zeal’?

This description of Tony Blair’s ambitions by Alastair Campbell invites a question I’ve often wondered about. What is ‘modernising zeal’? It’s such a loaded term but clearly so significant to understand centrists dispositions yet it’s rarely, if ever, defined:

But he feared that unless the party adapted to the modern post-Cold War, post-Thatcherite world, it would ossify and die. He was always pushing at the outer edge of modernisation. That modernising zeal was what ultimately made the offer to work for him irresistible.