How can Newton's first law be applied to the concept of inertia in physics?

Newton's first law states that an object at rest will stay at rest, and an object in motion will stay in motion with the same speed and direction unless acted upon by an external force. This law can be applied to the concept of inertia in physics, as inertia is the tendency of an object to resist changes in its motion. Objects with more mass have greater inertia, making them harder to accelerate or decelerate. This is because the object's mass resists changes in its velocity, in accordance with Newton's first law.