Because Static Friction and Inertia can be confused, because mass defines how much inertia a body has, that is, the difficulty of putting some acceleration in it. And it's basically the same with friction. Static friction says that, for example, for you to pull a table with your hands, you need to put force (obviously), as measured by Newtons. From the Newton that the table start to accelerate, then there is the static friction.
For example:
To speed up the table, you put five Newtons, and the table does not move. Put ten, still not moving. It puts 11, and it begins to move (accelerate). So the static friction force is 10 Newtons.
