A soft and spongy feeling brake pedal is usually caused by air in the brake lines or by low brake fluid levels, both of which compromise the car's braking ability as the pressure applied to the brake pedal is not fully transmitted to the brakes on each wheel.
If your brake pedal feels soft or spongey you should book a Brake Fluid Flush to bleed the trapped air out of the system, completely renewing the entire braking system with new premium brake fluid.