A body at rest does not mean absence of any force. The body, in question, could actually experience a system of force whose net force is zero.
Consider a book lying on a table. The book experiences two forces:
1. Its weight acting downwards, and
2. Normal reaction of the table acting upwards.
These two forces are equal and opposite to each other, hence their resultant is zero.
It means that first law of motion provides additional possibility of rest other than when rest may result from “No Force” being applied to the body.
This part of the law, therefore, characterizes two important aspects of rest as:
• Rest may arise from no force being applied on the body.
• Rest may arise from zero net force being applied on the body
These points require further deliberations.