The mind is the barrier because the mind holds the obstacles. The obstacles are in the form of past memories of rejections betrayals hurts. When the fire of love arises these obstacles begin swirling in the fire. The fire must burn brighter for these obstacles to be heated to the point of combustion. No matter what the nature of the obstacle it will find a fire hot enough to consume itself.
Obstacles are sentient.
They long to be free. Their longing has power. We brighten the fire by surrendering to it what we falsely imagine ourselves to be. These are our conditions and reasons. They are rooted in fear and disappointment.