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Ensuring that help is on the way while performing Basic Life Support (BLS) in the park is crucial because it maximizes the victim's chances of survival and recovery. 

While immediate CPR and the use of an Automated External Defibrillator (AED) can temporarily sustain blood flow and oxygenation, professional medical intervention is essential for advanced care and definitive treatment. Calling emergency services ensures that paramedics equipped with life-saving medications, advanced airway management tools, and the expertise to provide comprehensive medical care are en route. 

This coordination allows for a seamless transition from basic to advanced life support, reducing the time to definitive care, which is critical in improving outcomes for the victim. Moreover, having emergency services on the way provides psychological reassurance to the rescuer, enabling them to focus on delivering high-quality CPR and AED use while knowing that professional help is imminent.