The cage is the ego, the bird is the soul, desires are the bars of the cage and the lock is ignorance. The stifling feeling is the sign that the soul within has grown up sufficiently and wants to get rid of the bondage to ignorance and the old mechanical life centred around the ego and the little self. It seeks to enter into the vastness of God. Aspiration is the key and the power to turn it into the lock and open the cage is the Grace.
Affectionately,
Alok Da