1st law of newton
It state that unless an external force act on a body it remain same on rest or motion.
A object will remain at rest or motion until and unless an external force is applied on it
Accor. to it, a body continues its state of rest or uniform motion unless it is acted upon by some external force to change its state. This law is law of inertia.
First law is the law of inertia. Inertia is property of objects to resist change ...if it is in rest it wants to be in rest and if it is in motion it want to remain in motion