What comes first? Strategy or structure? According to Peter Drucker it's a no brainer.
"Only a clear definition of the mission (purpose) makes possible clear and realistic business objectives. It is the foundation for priorities, strategies, plans and work assignments…Structure follows strategy. Strategy determines what the key activities are in a given business. And strategy requires knowing what our business is and what it should be (p. 162, Inside Drucker's Brain)."
What if your organization is working with a legacy structure? If you want to accomplish your mission you'll need to start there, formulate strategy to do what needs to be done…and then align structures to make the strategy happen.