The mission statement guides the day-to-day operations and decision-making of the organization. It helps in tactical planning and "rallying the troops" around a common near- to medium-term goal. The mission statement helps members of the organization get on the same page on what they should do and how they should do it.
The vision statement is, in a sense, loftier. It outlines the worldview of the organization and why it exists. It attracts people — not just employees but also customers and vendors — who believe in the vision of the organization.