Rahu becomes visible only when it exists with the sun or the moon. Likewise the Soul is apprehended only when it exists with the body.
यथा चन्द्रार्कसंयुक्तं तमस्तदुपलभ्यते। तद्वच्छरीरसंयुक्तः शरीरीत्युपलभ्यते॥