Why is it necessary to insert resistance in series with the motor armature when starting a dc motor?

Inserting resistance in series with the motor armature when starting a DC motor is necessary to limit the inrush current. At startup, the motor has low back electromotive force (EMF) due to its initial stationary state, leading to a potentially very high current that could damage the motor windings or the power supply. The resistance helps to gradually increase the current as the motor accelerates, allowing it to reach its operational speed safely. Once the motor is up to speed, the resistance can be removed or reduced to improve efficiency.